Semiconductor device having radiation structure

ABSTRACT

A semiconductor device includes two semiconductor chips that are interposed between a pair of radiation members, and thermally and electrically connected to the radiation members. One of the radiation members has two protruding portions and front ends of the protruding portions are connected to principal electrodes of the semiconductor chips. The radiation members are made of a metallic material containing Cu or Al as a main component. The semiconductor chips and the radiation members are sealed with resin with externally exposed radiation surfaces.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of application Ser. No.09/717,227, which was filed on Nov. 22, 2000 now U.S. Pat. No. 6,703,707and which was based upon and claimed the benefit of Japanese PatentApplications No. 11-333119 filed on Nov. 24, 1999, No. 11-333124 filedon Nov. 24, 1999, No. 2000-88579 filed on Mar. 24, 2000, No. 2000-97911filed on Mar. 30, 2000, No. 2000-97912 filed on Mar. 30, 2000 and No.2000-305228 filed on Oct. 4, 2000, the contents of which areincorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a semiconductor device in which heat isradiated from both sides of a semiconductor chip accommodated therein.

2. Description of the Related Art

For example, JP-A-6-291223 discloses a semiconductor device in whichheat is radiated from both sides of a semiconductor chip. FIGS. 1A to 1Cshow this semiconductor device. As shown in the figures, a pair ofradiation members J2, J3 sandwich several semiconductor chips J1, andare thermally and electrically connected to the semiconductor chips J1.The several semiconductor chips J1 arranged on a plane and the radiationmembers J2, J3 are sealed with resin J5.

Each of the radiation members J2, J3 serves as an electrode, and has asurface exposed from the resin J5 at an opposite side of the facecontacting the semiconductor chips J1. Each of the radiation members J2,J3 performs radiation of heat by making the exposed surface contact acontact body (not shown) that can exhibit a radiation action. A controlterminal J4 connected with a control electrode of the semiconductorchips J1 protrudes to an outside from the resin J5.

Used as the radiation members J2, J3 is W (tungsten) or Mo (molybdenum)having a thermal expansion coefficient approximate to that of thesemiconductor chips J1. The radiation member J2 that is connected to thesurfaces of the semiconductor chips J1 on which the control electrode isformed is an emitter electrode, and the radiation member J3 that isconnected to the surfaces of the semiconductor chips J1 at an oppositeside of the control electrode is a collector electrode.

Besides, several solder bumps J7 protrudes from an insulating plate J6that has a through hole at a center thereof in which the radiationmember J2 penetrates as the emitter electrode. The solder bumps J7 arebonded to bonding pads existing in unit patterns of the respectivesemiconductor chips J1 disposed on the radiation member J3 as thecollector electrode.

When the radiation members J2, J3 serving also as electrodes are made ofmetallic material such as W or Mo having linear thermal expansioncoefficient approximate to that of the semiconductor chips J1 made of Si(silicon), these metallic materials are, in electrical conductivityabout one third of that of Cu (copper) or Al (aluminum), and in thermalconductivity about one third to two third thereof. Thus, in the presentcircumstances involving an increased requirement for flowing a largecurrent in the semiconductor chip, using W or Mo as a member that servesas a radiation member and an electrode simultaneously causes manyproblems.

Also, in general, a larger chip is required to accommodate a largercurrent. However, there are many technological problems to increase thechip size, and it is easier to manufacture plural smaller chips andaccommodate them into one package.

In the technique disclosed in the publication describe above, theseveral semiconductor chips J1 are formed in the semiconductor device.However, as shown in FIG. 1A, because the radiation member J2 has asimple rectangular shape, and is provided at the center of the device,disposal of different semiconductor chips in one device is limited. Thatis, when the semiconductor chips are different from one another in, forexample, thickness, it is difficult for the one emitter electrode havinga simple shape to be connected to all of the different semiconductorchips.

SUMMARY OF THE INVENTION

The present invention has been made in view of the above problem. Anobject of the present invention is to improve a radiation property andan electrical conductivity of a semiconductor device including radiationmembers that are thermally and electrically connected to both surfacesof a semiconductor chip therein. Another object of the present inventionis to provide a semiconductor device easily accommodating severaldifferent semiconductor chips therein.

For example, according to one aspect of the present invention, in asemiconductor device in which a semiconductor chip is thermally andelectrically connected to first and second radiation memberstherebetween, the first and second radiation members are made of ametallic material that is superior to tungsten and molybdenum in atleast one of an electrical conductivity and a thermal conductivity.Accordingly, the radiation property and the electrical conductivity ofthe semiconductor device can be improved.

According to another aspect of the present invention, in a semiconductordevice in which first and second semiconductor chips are thermally andelectrically connected to first and second radiation memberstherebetween, the first radiation member has first and second protrudingportions protruding toward the first and second semiconductor chips, andfirst and second front end portions of the first and second protrudingportions are thermally and electrically connected to the first andsecond semiconductor chips through a bonding member.

In this case, even when the first and second semiconductor chips aredifferent from each other in thickness, the first and second radiationmembers can be provided with first and second radiation surfacesapproximately parallel to each other by controlling protruding amountsof the first and second protruding portions.

According to still another aspect of the present invention, in asemiconductor device in which a semiconductor chip is disposed between afirst conductive member and a second conductive member, the firstconductive member is further bonded to a third conductive member at anopposite side of the semiconductor chip so that a bonding area betweenthe first conductive member and the third conductive member is smallerthan that between the first conductive member and the semiconductorchip. Accordingly, stress concentration on the first conductive membercan be suppressed to prevent occurrence of cracks. This results inimproved radiation property and electrical conductivity of thesemiconductor device.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects and features of the present invention will become morereadily apparent from a better understanding of the preferredembodiments described below with reference to the following drawings, inwhich;

FIG. 1A is a schematic view showing a semiconductor device according toa prior art;

FIG. 1B is a cross-sectional view showing the semiconductor device,taken along line IB—IB in FIG. 1A;

FIG. 1C is a cross-sectional view showing the semiconductor device,taken along line IC—IC in FIG. 1A;

FIG. 2A is a cross-sectional view showing a semiconductor device in afirst preferred embodiment;

FIG. 2B is an enlarged cross-sectional view showing a part indicated byarrow IIB in FIG. 2A;

FIG. 3 is a table showing metals usable for a radiation member in thefirst embodiment;

FIG. 4A is a cross-sectional view partially showing a semiconductordevice in a second preferred embodiment;

FIGS. 4B to 4D are cross-sectional views respectively showing a firstside radiation member and a a Si chip in the second embodiment;

FIGS. 5A to 5C are cross-sectional views respectively taken along linesVA—VA, VB—VB, and VC—VC in FIGS. 4B to 4D;

FIG. 6 is a cross-sectional view showing a semiconductor device in athird preferred embodiment;

FIG. 7 is a cross-sectional view showing a semiconductor device in afourth preferred embodiment;

FIG. 8A is a cross-sectional view showing a semiconductor device in afifth preferred embodiment;

FIG. 8B is a cross-sectional view taken along line VIIIB—VIIIB in FIG.8A;

FIG. 9A is a cross-sectional view showing a semiconductor device in asixth preferred embodiment;

FIG. 9B is an enlarged cross-sectional view showing a part indicated byarrow IXB in FIG. 9A;

FIG. 9C is a cross-sectional view showing an example in the sixthembodiment;

FIG. 10 is a cross-sectional view showing a semiconductor device in aseventh preferred embodiment;

FIG. 11 is a cross-sectional view showing a semiconductor device in aneighth preferred embodiment;

FIG. 12 is a cross-sectional view showing a semiconductor device in aninth preferred embodiment;

FIG. 13 is a cross-sectional view showing a semiconductor device in atenth preferred embodiment;

FIGS. 14A to 14C are cross-sectional views showing a method formanufacturing the semiconductor device shown in FIG. 13 in a stepwisemanner;

FIG. 15 is a cross-sectional view schematically showing a second leadmember and a soldering member as a modified example of the tenthembodiment;

FIG. 16 is a cross-sectional view schematically showing a method formanufacturing a semiconductor device in an eleventh preferredembodiment;

FIG. 17 is a cross-sectional view schematically showing a method formanufacturing a semiconductor device in a twelfth preferred embodiment;

FIG. 18 is a cross-sectional view schematically showing another methodfor manufacturing the semiconductor device in the twelfth embodiment;

FIG. 19 is a cross-sectional view showing a semiconductor device in athirteenth preferred embodiment;

FIGS. 20A to 20C are cross-sectional views for explaining a method formanufacturing the semiconductor device shown in FIG. 19;

FIG. 21 is a cross-sectional view showing a semiconductor device in afourteenth preferred embodiment;

FIG. 22 is a cross-sectional view showing a semiconductor device in afifteenth preferred embodiment;

FIG. 23 is a cross-sectional view showing a semiconductor device as amodification of the thirteenth embodiment;

FIG. 24 is a cross-sectional view showing a semiconductor device in asixteenth preferred embodiment;

FIG. 25 is an enlarged cross-sectional view showing a part surrounded bya broken line in FIG. 24;

FIG. 26 is a top plan view showing the semiconductor device in adirection indicated by arrow XXVI in FIG. 24;

FIG. 27 is a top plan view showing a semiconductor device in aseventeenth preferred embodiment;

FIG. 28A is a cross-sectional view showing the semiconductor device,taken along line XXVIIIA—XXVIIIA in FIG. 27;

FIG. 28B is a cross-sectional view showing the semiconductor device,taken along line XXVIIIB—XXVIIIB in FIG. 27;

FIG. 29 is a diagram showing an equivalent circuit of an IGBT chip inthe semiconductor device in the seventeenth embodiment;

FIGS. 30A to 30D are schematic views showing a method for manufacturingradiation members in the seventeenth embodiment;

FIG. 31 is a schematic view showing a constitution observed in a sidedirection in a manufacturing process of the semiconductor device;

FIGS. 32A to 32C are schematic views showing a step for caulkingfixation;

FIG. 33 is a cross-sectional view partially showing an IGBT chip as anexample;

FIG. 34 is a cross-sectional view showing a semiconductor device in aneighteenth preferred embodiment;

FIGS. 35A and 35B are cross-sectional views showing a radiation memberused in a modified example of the eighteenth embodiment; and

FIG. 36 is a cross-sectional view showing a semiconductor device in amodified embodiment of the seventeenth embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

(First Embodiment)

A first preferred embodiment is described with reference to FIGS. 2A and2B. As shown in FIG. 2A, a pair of radiation members 2, 3 are disposedto sandwich two Si chips 1 a, 1 b that are disposed on a plane. Theradiation members 2, 3 are thermally and electrically connected toprincipal electrodes of the Si chips 1 a, 1 b through bonding members 4.Hereinafter, connection means thermal and electrical connection exceptcases in which specific descriptions are presented. A control electrodeof the Si chip 1 a is electrically connected to a control terminal 5,which is connected to a lead frame, via a wire 8 formed by wire bonding.

Specifically, the radiation member (first side radiation member) 2,facing upper surfaces (first surfaces) 6 a of the Si chips 1 a, 1 b towhich the wire bonding is performed is formed with protruding portions 2a protruding at a step-like shape at positions facing the principalelectrodes of the Si chips 1 a, 1 b. Front ends of the protrudingportions 2 a are generally flat and the flat portions are respectivelyconnected to the principal electrodes through the bonding members 4.Being generally flat means flat at a level that does not interfere withbonding between the protruding portions 2 a and the principalelectrodes.

Next, the protruding portions 2 a are explained in more detail. As shownin FIG. 2B, when the Si chips 1 a, 2 b are power devices, each withstandvoltage at peripheral portions of the Si chips 1 a, 1 b is kept by guardrings 7 that is provided on one surface of each chip, i.e., on thesurface 6 a or a surface (second surface) 6 b opposed to the surface 6a.

Like the present embodiment, when metallic materials as the radiationmembers 2, 3 are bonded to the both surfaces of each Si chip 1 a, 1 b,the radiation member 2 is bonded to the surface (the first surfaces inthis embodiment) 6 a where the guard rings 7 are provided. However,referring to FIG. 2B, a distance indicated by an arrow B at theperipheral portions of the Si chips 1 a, 1 b, i.e., at the regions oneof which is indicated by a broken line in the figure, the first sideradiation member 2 must be electrically insulated from the guard rings 7and from the edge surfaces of the Si chips 1 a, 1 b. Therefore,insulated regions must be provided there.

Because of this, the radiation member 2 has the protruding portions 2 aat-the-positions-facing the principal electrodes of the Si chips 1 a, 1b. In other words, the radiation member 2 has recess portions at thepositions facing the guard rings 7 of the Si chips 1 a, 1 b to avoid thehigh withstand regions (insulated regions).

The radiation member (second side radiation member) 3 bonded to theother surfaces 6 b of the Si chips 1 a, 1 b has no protruding portion,and is generally flat. That is, the second side radiation member 3 isgenerally so flat that it does not interfere with mountability of the Sichips 1 a, 1 b to the radiation member 3. In the respective radiationmembers 2, 3, respective surfaces opposite to the surfaces facing the Sichips 1 a, 1 b constitute radiation surfaces 10 that are also generallyflat and are approximately parallel to each other.

Here, in this embodiment, the wire-bonded Si chip is an IGBT (InsulatedGate Bipolar Transistor) 1 a, while the other Si chip is a FWD(free-wheel diode) 1 b. In the IGBT 1 a, the first side radiation member2 is an emitter, the second side radiation member 3 is a collector, andthe control electrode is a gate. As shown in FIG. 2A, the thickness ofthe FWD 1 b is larger than that of the IGBT 1 a. Therefore, in the firstside radiation member 2, the protruding portion 2 a facing the IGBT 1 ahas a protruding amount relatively larger than that of the otherprotruding portion 2 a facing the FWD 1 b.

As the first side and second side radiation members 2, 3, for example, ametallic material including Cu or Al-as a main component can be used,which has electrical conductivity and thermal conductivity larger thanthose of W and Mo, and is cheaper that those. FIG. 3 is a table showingexamples of metallic materials usable as the radiation members 2, 3. Asshown in FIG. 3, the radiation members 2, 3 can be made of one of metal“a” to metal “l”, anoxia copper, and the like. Here, for example, metal“a” is an alloy containing, in mass ratio, Fe (iron) at 2.3%, An (zinc)at 0.1%, P (phosphorous) at 0.03%, and Cu as the remainder.

The bonding members 4 are preferable to have a shear strength superiorto a shear stress produced by thermal stress, and to be superior in boththermal conductivity and electrical conductivity. As such conductivemembers 4, for example, solder, brazing filler metal, or conductiveadhesive can be used. The wire 8 for wire bonding can be made of Au(gold), Al, or the like which is used for wire bonding in general.

Also, as shown in FIG. 2A, these members 1 to 5, and 8 are sealed withresin 9 while exposing the radiation surfaces 10 of the radiationmembers 2, 3 at the opposite side of the Si chips 1 a, 1 b, and exposingsimultaneously the control terminal 5 at the opposite side of the wirebonding. The radiation surfaces 10 of the respective radiation members2, 3 serve as electrodes and perform radiation of heat simultaneously.The resin 9 preferably has a thermal expansion coefficient approximateto those of the radiation members 2, 3. For example, epoxy based moldresin can be used as such resin 9.

Further, the resin-sealed members 1 to 5 and 8 are sandwiched by a pairof outside wiring members 11 so that the radiation surfaces 10 contactthe outside wiring members 11. Each of the outside wiring members 11 isa flat plate having a portion with a plate shape or a fine wire shapethat is conducted to be interconnected with an outside. The outsidewiring members 11 and the resin-sealed members 1 to 5, and 8 are furthersandwiched by a pair of outside cooling members 13 with plate-shapedhigh thermal conductivity insulating substrates 12 interposedtherebetween. The resin-sealed members 1 to 5 and 8, the outside wiringmembers 11, the high thermal conductivity insulating substrates 12, andthe outside cooling members 13 are fixed by volts 4 or the like screwedfrom the outside cooling members 13.

The outside wiring members 11 may be made of any materials provided thatthey are superior in thermal conductivity and electrical conductivity.The high thermal conductivity insulating substrates 12 can be made of,for example, one of AlN (aluminum nitride), SiN (silicon nitride), Al₂O₃(aluminum dioxide), SiC (silicon carbide), BN (boron nitride), diamondor the like. The outside cooling members 13 is constructed to include aradiation fin, or to be cooled by water.

According to the constitution described above, as to an electrical path,current flow in the order of the outside wiring member 1 contacting thefirst side radiation member 2, the first side radiation member 2, the Sichips 1 a, 1 b, the second side radiation member 3, the outside wiringmember 11 contacting the second side radiation member 3 or in theinverse order. As to a thermal path, heat produced in the Si chips 1 a,1 b is transferred to the first side and second side radiation members2, 3, the outside wiring members 11, the high thermal conductivityinsulating substrates 12, and the outside cooling members 13, and thenis radiated.

Next, a method for manufacturing the semiconductor device shown in FIGS.2A and 2B is explained. First, the principal electrodes on the secondsurfaces 6 b of the Si chips 1 a, 1 b are bonded to the second sideradiation member 3 through the bonding members 4. Next, the controlelectrode of the Si chip 1 a and the control terminal 5 are electricallyconnected to each other by wire bonding. After that, the principalelectrodes on the first surfaces 6 a of the Si chips 1 a, 1 b are bondedto the front ends of the protruding portions 2 a of the first sideradiation member 2 by bonding members 4. Here, the protruding portions 2a of the first side radiation member 2 are formed by pressing or thelike previously.

Subsequently, a die (not show) is prepared, and the integrated Si chips1 a, 1 b and the first side and second side radiation members 2, 3 aredisposed in the die and is sealed with resin. Accordingly, electricalinsulation between the radiation members 2, 3 can be attained.Successively, as described above, with respect to the radiation surfaces10, the outside wiring members 11, the high thermal conductivityinsulating substrates 12, and the outside cooling members 13 aredisposed in this order. Then, the outside cooling members 13 arefastened with volts, so that the members 11 to 13 are fixed. Inconsequence, the semiconductor device in the present embodiment iscompleted.

According to the present embodiment, because the first side and secondside radiation members 2, 3 are made of metallic material containing Cuor Al as a main component that is superior in thermal conductivity andelectrical conductivity, the semiconductor device can be provided withimproved radiation property and improved electrical conductivity.Further, because these members can be manufactured at lower cost ascompared to a conventional case using W or Mo, the semiconductor devicecan be provided at low cost. Furthermore, the metallic materialcontaining Cu or Al as the main component is so soft as compared to W orMo that workability for forming the protruding portions 2 a on the firstside radiation member 2 is good.

Besides, because the protruding portions 2 a are provided on the firstside radiation member 2 and are connected to the respective different Sichips 1 a, 1 b, the connection between the respective Si chips 1 a, 1 band the radiation member 2 can be performed appropriately. Specifically,the protruding amounts and the shapes of the protruding portions 2 canbe changed in accordance with the thicknesses of the Si chips 1 a, 1 band the shapes of the principal electrodes of the Si chips 1 a, 1 b.Because of this, the different semiconductor chips 1 a, 1 b can beeasily accommodated in the semiconductor device.

The radiation surfaces 10 of the radiation members 2, 3 may haveirregularities thereon or may not be parallel to each other. However, inthis embodiment, the radiation surfaces 10 are made flat andapproximately parallel to each other. This is made possible because thesurface step, i.e., the difference in thickness between the Si chips 1a, 1 b can be absorbed by the protruding portions 2 a by controlling theprotruding amounts thereof in accordance with the respective thicknessesof the Si chips 1 a, 1 b.

As a result, in the present embodiment, because the radiation surfaces10 are generally flat and approximately parallel to each other, when thevolts are fastened to the radiation surfaces 10 with the outside wiringmembers 11, the high thermal conductivity insulating substrates 12, andthe outside cooling members 13 interposed therebetween, the surfaces 10and these members 11 to 13 can be brought in contact with each othersecurely and easily at the interfaces thereof.

Moreover, because the radiation surfaces 10 are approximately parallelto each other, a force produced by fastening the volts is uniformlyapplied to the members 1 to 5, 8, 9, and 11 to 13. Therefore, thesemembers 1 to 5, 8, 9, and 11 to 13 are not damaged or destroyed bydeviation of the force, and the assembling performance can be improved.

In general, though the IGBT 1 a and the FWD 1 b are used as a pair, asthe distance between the IGBT 1 a and the FWD 1 b is decreased, anoperation on a circuit becomes more ideal. According to the presentembodiment, because the IGBT 1 a and the FWD 1 b are disposed adjacentlyto each other in the integrally resin-sealed semiconductor device, theoperation of the IGBT 1 a can approach the ideal state in thesemiconductor device.

When the object of the invention is limited to provide a semiconductordevice capable of accommodating the different semiconductor chips 1 a, 1b easily, the materials for forming the first side and second sideradiation members 2, 3 are not limited to the materials containing Cu orAl as a main component but may be other conductive materials havingelectrical conductivity. That is, when the prevention of breakage of thebonding members 4 caused by thermal stress is of greater importance, thefirst side and second side radiation members 2, 3 should be made ofmetallic material having a thermal expansion coefficient approximate tothat of the Si chips 1 a, 1 b. On the other hand, when the radiationproperty and the electrical conductivity are of greater importance, theradiation members 2, 3 should be made of metallic material containing Cuor Al as a main component.

The resin 9 used in the present embodiment not only insulates theradiation-members 2, 3 from each other but also reinforces the bondingbetween the radiation members 2, 3 and the Si chips 1 a, 1 b byconnecting the radiation members 2, 3 to the Si chips 1 a, 1 b.Therefore, even when the radiation members 2, 3 are made of a metallicmaterial containing Cu or Al as a main component, which has a thermalexpansion coefficient different from that of the Si chips 1 a, 1 b, thebreakage of the bonding members 4 caused by thermal stress can berelaxed by the resin 9.

Especially when the resin 9 has a thermal expansion coefficientapproximate to that of the radiation members 2, 3, stress is applied tothe Si chips 1 a, 1 b to promote expansion and contraction similar tothose of the radiation members 2, 3 when temperature varies. Therefore,stress applied to the bonding members 4 is relaxed and generation ofstrain is restricted, resulting in improvement of reliability at theconnection portions.

Incidentally, although the second side radiation member 3 has noprotruding portion thereon in the present embodiment, it may have aprotruding portion. Thermal conductive grease or the like may be appliedto the contact faces between the outside wiring members 11 and the highthermal conductivity insulating substrates 12, and between the highthermal conductivity insulating substrates 12 and the outside coolingmembers 13 to enhance thermal bonding further.

The contact between each outside wiring member 11 and each high thermalconductivity insulating substrate 12 is preferable to be fixed bypinching as in the present embodiment in consideration of the differencein thermal expansion coefficient between the members 11 and 12. However,each radiation surface 10 and each outside wiring member 11 can beconnected by solder, brazing filler metal or the like because thesemembers can be made of materials having thermal expansion coefficientnot largely different from each other.

The body of the first side radiation member 2 may be separated from theprotruding portions 2 a. For example, the protruding portions 2 a may bebonded to a plate-shaped body of the member 2 by soldering, welding, orthe like. The material forming the first side radiation member 2 is notalways necessary to be identical with that forming the second sideradiation member 3. In the present embodiment, although theresin-sealing is performed by a die, the sealing may be performed bypotting without any die.

Although it is described that the resin 9 for sealing has a thermalexpansion coefficient approximate to those of the first side and secondside radiation members 2, 3, the resin 9 is not limited to that, but maybe other appropriate resin when there is no need to consider bondingstrength between the Si chips 1 a, 1 b and the radiation members 2, 3.

Although it is described in the present embodiment that the IGBT 1 a andthe FWD 1 b-are used as the Si chips, in some cases such as that onlyone Si chip is used, or the same kind of Si chips are used, theconnecting structure between the Si chip(s) and the radiation members 2,3 is not complicated. In these cases, the protruding portions 2 a neednot be formed on one of the radiation members 2, 3. As described above,the semiconductor device having improved radiation property andelectrical conductivity can be provided by forming the radiation members2, 3 from a metallic material containing Cu or Al as a main componenthaving electrical conductivity and thermal conductivity higher thanthose of W or Mo.

(Second Embodiment)

A second preferred embodiment differs from the first embodiment in aninside shape of the first side radiation member 2. FIG. 4A shows asemiconductor device in the second embodiment, and FIGS. 4B to 4D arecross-sectional views partially showing various first side radiationmembers 2 and Si chips 1 a, 1 b facing the respective radiation members2. FIGS. 5A to 5C are cross-sectional views respectively taken alonglines VA—VA, VB—VB, VC—VC in FIGS. 4B to 4D.

In FIG. 4A, the first side radiation member 2 is partially omitted, andthe cross-sectional shapes shown in FIGS. 4B to 4D are applicable to theomitted part. FIG. 4A also omits the outside wiring members 11, the highthermal conductivity insulating substrates 12, and the outside coolingmembers 13. Hereinafter, different portions from those in FIG. 2A areexplained. In FIGS. 4A to 4D and 5A to 5C, the same parts as those inFIG. 2A are indicated with the same reference numerals, and thoseexplanation is made simple.

As shown in FIGS. 4A to 4D and 5A to 5C, the first side radiation member2 has a space 15 at a portion connected to the Si chips 1 a, 1 b. Thespace 15 can have a lattice shape as in an example shown in FIG. 5A, becomposed of several concentric circles as in an example shown in FIG.5B, and be composed of several concentric rectangles as in an exampleshown in FIG. 5C. The shape of the space 15 in a direction perpendicularto the connection surface between the radiation member 2 and the Sichips 1 a, 1 b is as shown in FIG. 4B, 4C, or 4D. That is, there arecases where the space 15 is open at the connecting portions with the Sichips 1 a, 1 b, is open at the radiation surface 10, and is closed bothat the connecting portions with the Si chips 1 a, 1 b and the radiationsurface 10.

The space 15 can be formed by, for example, cutting work. When the space15 is closed both at the connecting portions with the Si chips 1 a, 1 band the radiation surface 10 as shown in FIG. 4D, it can be formed byforming the radiation member with the space opened at the connectingportions with the Si chips 1 a, 1 b by cutting first as shown in FIG.4B, and then by bonding a metal plate to close the opening portions bywelding or the like.

According to the present embodiment, the same effects as those describedin the first embodiment can be attained. In addition, the space 15formed in the first side radiation member 2 increases the rigidity ofthe radiation member 2. As a result, stress applied to the Si chips 1 a,1 b and to the bonding members 4 can be reduced, so that the breakage ofthe Si chips 1 a, 1 b can be prevented and the reliability in thebonding between the Si chips 1 a, 1 b and the radiation member 2 can beenhanced.

The other features not described in the second embodiment aresubstantially the same as those in the first embodiment. The space 15 isexemplified in cases it extends in the thickness direction of the Sichips 1 a, 1 b; however, it may extend in a surface direction of thechips 1 a, 1 b. Further, the space 15 may be formed in the second sideradiation member 3. The space 15 needs not be formed uniformly at theportions contacting the Si chips 1 a, 1 b, and can be arrangedappropriately at required positions.

The shape of the space 15 is not limited to the examples shown in thefigures, provided that it can reduce the rigidity of the radiationmember. When the radiation members 2, 3 are made of a metallic materialincluding Cu or Al, it is easy to form the space 15 because theradiation members 2, 3 are easy to be processed.

(Third Embodiment)

FIG. 6 shows a semiconductor device in a third preferred embodiment, inwhich the outside wiring members 11, the high thermal conductivityinsulating substrates 12, and the outside cooling members 13 shown inFIG. 2A are omitted. Hereinafter, different portions from those in thefirst embodiment are mainly explained, and in FIG. 6, the same parts asthose in FIG. 2A are indicated with the same reference numerals.

As shown in FIG. 6, in the third embodiment, metallic members (partiallydisposed metallic members) 16 made of Mo, W, Cu—Mo, or the like having athermal expansion coefficient approximate to that of Si chips aredisposed at the portions of the first side and second side radiationmembers 2, 3 facing the Si chips 1 a, 1 b. The partially disposedmetallic members 16 can be previously formed on the radiation members 2,3 by soldering, brazing, shrinkage fitting, or press-fitting. Toposition the partially disposed metallic members 16 with respect to theSi chips 1 a, 1 b with high accuracy, the Si chips 1 a, 1 b and thepartially disposed metallic members 16 should be bonded by soldering,brazing, or the like, previous to the bonding between the partiallydisposed metallic members 16 and the radiation members 2, 3 bysoldering, brazing, or the like.

According to the present embodiment, the same effects as those in thefirst embodiment can be attained. In addition, because the thermalexpansion coefficient at the connecting portions between the Si chips 1a, 1 b and the first side and second side radiation members 2, 3 areapproximated to each other, thermal stress produced by a change intemperature can be reduced at the connecting portions and the bondingstrength can be enhanced. Also, the addition of the metallic members 16having the thermal expansion coefficient approximate to that of the Sichips 1 a, 1 b approaches the strain of the radiation members 2, 3 as awhole to Si, so that stress applied to the Si chips 1 a, 1 b can belowered.

Accordingly, the semiconductor device can be provided with highreliability to the bonding strengths between the Si chips 1 a, 1 b andthe radiation members 2, 3 and without breakage of the Si chips 1 a, 1 bwhile securing the same effects as those in the first embodiment.Incidentally, the other features not described in this embodiment aresubstantially the same as those in the first embodiment. The partiallydisposed metallic members 16 need not be provided at the entire regionof each radiation member 2 or 3 connected to the Si chips 1 a, 1 b. Thepartially disposed metallic members 16 should be disposed at necessarypositions appropriately. Also, in this embodiment, the space 15 may beformed in at least one of the first side and second side radiationmembers 2, 3 as in the second embodiment.

(Fourth Embodiment)

FIG. 7 shows a semiconductor device in a fourth preferred embodiment.This embodiment relates to a modification of the outside wiring members11 described in the first embodiment. Hereinafter, different portionsfrom the first embodiment are mainly described, and in FIG. 7, the sameparts as those in FIG. 2A are indicated by the same reference numerals.In FIG. 7, the high thermal conductivity insulating substrates 12 andthe outside cooling members 13 are omitted.

As shown in FIG. 7, conductive terminals 17 connected to the principalelectrodes of the Si chips 1 a, 1 b are taken out of edges of the firstside and second side radiation members 2, 3 as main electrode terminalsto be electrically connected to an outside. The conductive members 17have the same function as that of the outside wiring members 11 shown inFIG. 2A.

The conductive members 17 protrude from the respective radiation members2, 3 from approximately the same position with respect to the respectivemembers 2, 3 and in an approximately identical direction that isperpendicular to the radiation surfaces 10. That is, the conductivemembers 17 are approximately parallel to each other, and accordingly canprevent a parasitic inductance described below. The root parts of theconductive members 17 are adjacent to each other. The semiconductordevice shown in FIG. 7 dispenses with the outside wiring members 11shown in FIG. 2A, and the radiation surfaces 10 contact the outsidecooling members 13 with the high thermal conductivity insulatingsubstrates 12 interposed therebetween, although they are not shown.

It is preferable that the respective radiation members 2, 3 and therespective conductive members 17 are integrated with each other inconsideration of electrical resistance. However, when the conductivemembers 17 are separately formed and bonded to the radiation members 2,3, screwing, welding, brazing, and soldering methods are conceivable forthe bonding. At that time, the conductive members 17 can be made ofvarious materials as long as it is superior in electrical conductivity.

According to the present embodiment, the same effects as those in thefirst embodiment can be exhibited. In addition, because electricalconnection with the outside can be made via the conductive members 17,it is not necessary to connect the outside wiring members 11 to theradiation surfaces 10 of the radiation members 2, 3. As a result, ascompared to the case where the outside wiring members 11 are used, thenumber of connecting interfaces in the direction in which heat istransferred is reduced to reduce heat resistance at the connectinginterfaces. Therefore, the radiating property is further improved. Inaddition, the thickness of the semiconductor device in the thicknessdirection of the Si chips 1 a, 1 b can be reduced, resulting in sizereduction of the semiconductor device.

As a more preferable configuration, in the present embodiment, theconductive members 17 are provided to be approximately parallel to eachother at adjacent positions, and in the semiconductor device, currentsflow in the respectively conductive members 17 with the same intensityin directions inverse to each other. When currents flow in the adjacentparallel conductive members in the inverse directions to each other,magnetic fields produced around the conductive members are canceled witheach other. As a result the parasitic inductance can be significantlysuppressed.

Also in the present embodiment, as in the first embodiment, theradiation members are made of a metallic material containing Cu or Al asa main component when the object of the invention is to improve theradiation property and the electrical conductivity. In this case,because workability of Cu and Al is good, the conductive members 17 canbe easily formed by pressing, cutting, or the like.

The other features not described in the present embodiment aresubstantially the same as those in the first embodiment. In the presentembodiment, although the conductive members 17 are adjacent to andapproximately parallel to each other, the conductive members 17 are notlimited to that, but may protrude from the respective radiation membersin different directions from each other. Also when the radiation members2, 3 use a material having high hardness such as W or Mo to easily sealthe several semiconductor chips with resin, the conductive members 17are preferably formed as separate members because they are difficult tobe integrally formed with the radiation members 2, 3.

(Fifth Embodiment)

FIGS. 8A and 8B show a semiconductor device in a fifth preferredembodiment, in which the outside wiring members 11, the high thermalconductivity insulating substrates 12, and the outside cooling members13 shown in FIG. 2A are omitted. The present embodiment differs from thefirst embodiment in the connecting method between the Si chips 1 a, 1 band the first side radiation member 2. Hereinafter, different portionsfrom the first embodiment are mainly explained and in FIGS. 8A and 8Bthe same parts as those in FIG. 2A are assigned to the same referencenumerals.

As shown in FIGS. 8A and 8B, bump-shaped bonding members 4 are uniformlyprovided between the principal electrodes on the principal surfaces 6 aof the Si chips 1 a, 1 b and the first side radiation member 2, andspaces provided among the bonding members 4 are filled with resin 18.The resin 18 has material properties similar to those of metal such asgood wettability, and prevents stress concentration on the bump-shapedbonding members 4. Hereinafter, the resin is referred to as RAB (ResistAssist Bonding) resin 18. The RAB resin 18 is specifically composed ofepoxy based resin mixed with silica fillers.

To form the constitution described above, like the semiconductor devicein the first embodiment, after the Si chips 1 a, 1 b are connected tothe second side radiation member 3 and the wire bonding are carried out,the bonding members 4 are formed in bump shapes on the principalelectrodes of the Si chips 1 a, 1 b at the side of the first surfaces 6a, and connected to the first side radiation member 2.

Successively, the RAB resin 18 is put in an injector, and is injectedinto the spaces provided among the bump-shaped bonding-members 4. Atthat time, even when the resin is not injected into all the spacesdirectly, the spaces can be filled with the resin due to a capillarytube phenomenon. After that, as described above, the integrated Si chips1 a, 1 b and the radiation members 2, 3 are put in the die, and aresealed with the resin 9 integrally.

According to the present embodiment, the same effects as those in thefirst embodiment can be attained. Further, the RAB resin 18 can restrictplastic deformation of the bonding members 4. Furthermore, the RBA resin18 can prevent cracks, which are produced in the bonding members 4 dueto thermal stress, from progressing. That is, the RBA resin 18strengthens the bonding between the Si chips 1 a, 1 b and the first sideradiation member 2, and increases the reliability in connection.

The features not described in the present embodiment are substantiallythe same as those in the first embodiment. Also in the presentembodiment, small bumps are arranged uniformly; however, smaller numberof bumps with larger size than those in the present embodiment may bearranged. Although the bump-shaped bonding members 4 are adopted forbonding the Si chips 1 a, 1 b to the first side radiation member 2 inthe present embodiment, they may be adopted for bonding the Si chips 1a, 1 b to the second side radiation member 3. If the mold resin 9 can beinjected into the spaces among the bumps to fill them completely, it isnot necessary to inject the RBA resin 18 previously. In this case, themold resin 9 filling the spaces among the bumps works as the RBA resin18. The second to fourth embodiments can be applied to the presentembodiment appropriately.

(Sixth Embodiment)

Hereinafter, sixth to ninth embodiments are described as first to fourthmodified examples of the embodiments described above, which areapplicable to the above respective embodiments, and some of which may becombined with each other to be applied to the above respectiveembodiments.

First, the sixth embodiment is explained referring to FIGS. 9A to 9C. Inthe above embodiments, the first side radiation member 2 is formed withthe protruding portions 2 a; however, as indicated by an arrow F in FIG.2B, because the first side radiation member 2 is thickened at theprotruding portions 2 a, its rigidity is increased. The larger therigidity of the first side radiation member 2 is, larger compressivestress is applied to the Si chips 1 a, 1 b.

To reduce the rigidity, a method shown in FIG. 9C is conceivable, inwhich the first side radiation member 2 is formed by embossing asufficiently thinned metallic plate to have a protruding portion foravoiding an insulated region, and is bonded to the Si chips 1 a, 1 bwith a decreased rigidity. However, in this method, because theradiation surface 10 of the first side radiation member 2 is not flat,it is difficult to contact the outside wiring member 11 and the outsidecooling member 13.

In this connection, in this embodiment as shown in FIGS. 9A and 9B, aninsulating film 20 is formed on the first side radiation member 2, withan opening pattern 19 opened at regions corresponding to the inner sidesof the Si chips 1 a, 1 b as compared to the peripheral portions of thechips 1 a, 1 b where the guard rings 7 are provided. In other words, theinsulating film 20 is formed at regions corresponding to the insulatedregions in FIG. 2B, and opened at regions corresponding to the principalelectrodes of the Si chips 1 a, 1 b at the side of the first surfaces 6a.

The insulating film 20 is preferable to be close without pinholes, andis necessary to withstand thermal contraction of the radiation member 2.A film made of polyimide or glass is applicable to such an insulatingfilm 20. When the semiconductor device in this embodiment ismanufactured, after the insulating film 20 is formed on the radiationmember 2, the Si chips 1 a, 1 b are bonded to the radiation member 2 atthe side of the first surfaces 6 a. The other steps are substantiallythe same as those for the semiconductor device in the first embodiment.

According to the method described above, the guard rings 7 can beelectrically insulated from the first side radiation member 2 by theinsulating film 20. The radiation member 2 can be formed in a plateshape without a protruding portion 2 a for avoiding the guard rings 7 ofthe Si chips 1 a, 1 b. In this case, the rigidity of the radiationmember 2 can be reduced by the decreased thickness of the radiationmember 2 as far as the radiation property is allowed. As a result, thecompressive stress applied to the Si chips 1 a, 1 b can be mitigated.

When the first side and second side radiation members 2, 3 do not haveany protruding portions, it can be suitably adopted in cases of one Sichip, and several Si chips having an identical thickness with eachother. Even when the several Si chips are different from one another inthickness, there is no problem if the difference in thickness can beabsorbed by the amounts of the bonding members 4.

The other features not described in this embodiment are substantiallythe same as those in the first embodiment. In this embodiment, theinsulating film 20 is formed on the first side radiation member 2;however, it may be formed on the second side radiation member 3. Ifthere is a region not filled with the resin 9 for sealing, theinsulation could not be securely attained by the resin 9. However, theinsulation can be securely provided by the insulating film 20 if it isformed on the region in advance. This prevention by the insulating film20 can be applied to the case where the radiation member 2 has theprotruding portions 2 a as well.

(Seventh Embodiment)

Next, the seventh embodiment is described as a second modified examplereferring to FIG. 10. In this embodiment, the electrical connectingmethod between the control terminal 5 and the control electrode of theSi chip 1 a differs, and FIG. 10 shows an example in which the presentembodiment is applied to the fourth embodiment (FIG. 7). Hereinafter,different portions from those in FIG. 7 are mainly discussed, and inFIG. 10 the same parts as those in FIG. 7 are assigned to the samereference numeral.

As shown in FIG. 10, the electrical connection between the controlelectrode and the control terminal 5 is provided by a bump 21 that ismade of, for example, solder, brazing filler metal, conductive adhesive,or the like. According to this modified example, the wire bonding stepneeds not be performed, and the control terminal 5 can be bondedsimultaneously with the bonding between the Si chips 1 a, 1 b and theradiation members 2, 3. Thus, the manufacturing process can besimplified. Also, wire flow of wire bond does not occur during the resinsealing.

(Eighth Embodiment)

Next, the eighth embodiment is described as a third modified examplereferring to FIG. 11. In this embodiment, the locations of the radiationsurfaces 10 differ. FIG. 11 is an example in which the presentembodiment is applied to the semiconductor device that is provided bycombining the first embodiment and the seventh embodiment being thesecond modified example. Hereinafter, different portions from those inFIGS. 2A and 10 are mainly described, and in FIG. 11 the same parts areassigned to the same reference numerals.

As shown in FIG. 11, in this embodiment, each of the first side andsecond side radiation members 2, 3 has a wedge shaped cross-section, andthe protruding portions 2 a are formed on the first side radiationmember 2. A side face of the first side radiation member 2 and a sideface of the second side radiation member 3 (disposed at a lower side inthe figure) serve as the radiation surfaces 10. The radiation surfaces10 of the first side and second side radiation members 2, 3 areapproximately perpendicular to the connecting surfaces of the radiationmembers 2, 3 being connected to the Si chips 1 a, 1 b, and are coplanarwith each other. The radiation surfaces 10 contact the outside coolingmember 13 via the high thermal conductivity insulating substrate 12, andare fixed by insulating volts 22.

According to the present embodiment, because there is no need to preparetwo outside cooling members 13, the flexibility for assembling thesemiconductor device with the outside cooling member 13 is improved. Forexample, the semiconductor device of the present invention isreplaceable with a conventional cooling system having a cooling part atonly one side. In addition, because the number of the high thermalconductivity insulating substrates 12 can be reduced to one, the cost ofparts can be reduced.

In the present embodiment, although the radiation surfaces 10 areperpendicular to the connecting surfaces of the radiation members 2, 3with the Si chips 1 a, 1 b, they can be attached to various types ofoutside cooling members by changing the angle appropriately. When theconductive members described in the fourth embodiment are used, theconductive members can be taken out of side faces of the radiationmembers 2, 3 different from the radiation surfaces 10.

(Ninth Embodiment)

Next, the ninth embodiment is explained as a fourth modified examplewith reference to FIG. 12. This embodiment differs in the fixing methodof the outside wiring members 11. Hereinafter, different portions fromthose in FIG. 2A are mainly described, and the same parts as those inFIG. 2A are assigned to the same reference numerals in FIG. 12.

As shown in FIG. 12, each four screw holes 23 a are formed in therespective first side and second side radiation members 2, 3 from theradiation surfaces 10 not to reach the Si chips 1 a, 1 b. Each of theoutside wiring members 11 has four screw holes 23 b penetrating it andcorresponding to the screw holes 23 a. Then, screws (not shown) areinserted into the screw holes 23 a, 23 b from surfaces of the outsidewiring members 11 at an opposite side of the respective radiationsurfaces 10. Accordingly, the radiation members 2, 3 and the outsidewiring members 11 are fixed together. Here, the screw holes 23 a, 23 bare formed by a drill or the like.

According to this embodiment, because the radiation members 2, 3 havethe screw holes 23 a not penetrating them, the screws do not contact theSi chips 1 a, 1 b, and the screw holes 23 a, 23 b can be formed atarbitrary positions. Also, because the fixation is achieved by thescrews, even when the pressure for fixing the outside wiring members 11to the respective radiation members 2, 3 is increased, no pressure isapplied to the Si chips 1 a, 1 b. As a result, the contact resistancesbetween the radiation members 2, 3 and the outside wiring members 11 canbe reduced, and the radiation property and the electrical conductivitycan be improved.

Especially, the screw fixation can be performed at the positions of thesecond side radiation member 3 immediately under the Si chips 1 a, 1 b.Therefore, thermal and electrical connection between the Si chips 1 a, 1b and the second side radiation member 3 can be secured. The thermalconnections of the semiconductor device to which the outside wiringmembers 11 are screwed, and the high thermal conductivity insulatingsubstrates 12 and the outside cooling members 13 can be provided, forexample, substantially in the same manner as in the first embodiment.One screw hole 23 a or 23 b is sufficient for each of the members 2, 3,and 11 to perform the fixation described above. This embodiment isapplicable to the above embodiments except the third modified example.

(Tenth Embodiment)

A semiconductor device in a tenth preferred embodiment is explained withreference to FIG. 13. This embodiment is made to improve a degree ofparallelization between two lead (radiation) members sandwiching asemiconductor element therebetween. Specifically, the semiconductordevice includes an IGBT element 101 and a diode 102 that form a circuitas semiconductor elements. The semiconductor elements 101, 102 arebonded to a surface 103 a of a plate-shaped first lead member (firstconductive member) 103 made of, for example, cupper, through firstsoldering members 104 composed of 10 wt % Sn (tin) and 90 wt % Pb (lead)and having a fusing point of 320° C. Block-shaped heat sinks 105 made ofcopper are respectively bonded to the semiconductor elements 101, 102through the first soldering members 104.

On the heat sinks 105, a second lead member (second conductive member)107 made of copper or the like is bonded at a surface 107 a thereofthrough second soldering members 106 having a fusing point lower thanthat of the first soldering members 104. The second soldering members 6contain, for example, Sn at 90 wt % or more, and have the fusing pointof 240° C.

The surface 103 a of the first lead member 103 and the surface 107 a ofthe second lead member 107 face each other with the semiconductorelements 101, 102 interposed therebetween, and extend approximately inparallel with each other (for example, an inclination between the leadmembers 103, 107 is 0.1 mm or less). Also, in this semiconductor device,an outer lead 108 and the IGBT element 101 are electrically connected toeach other by a bonding wire 109 made of Au or Al for electricalconnection with an outside.

The members 101 to 109 assembled as above are encapsulated and sealedwith mold resin 110 composed of, for example, epoxy resin, andaccordingly are protected from external environment. The other surfaces103 b, 107 b of the lead members 103, 107 are exposed from the moldresin 110, and serve as radiation surfaces.

Thus, in this semiconductor device, the circuit is composed of the twosemiconductor elements 101, 102, and the two lead members 103, 107 serveas electrodes simultaneously. Signal communication between thesemiconductor elements 101, 102 and the outside is performed through thelead members 103, 107, the wire 109, and the outer lead 108. The leadmembers 103, 107 also serve as radiation members, and facilitate heatradiation by, for example, disposing cooling members (not shown) on thesurfaces 103 b, 107 b through insulating members.

Next, a method for manufacturing the semiconductor device in the presentembodiment is explained with reference to FIGS. 14A to 14C. First, thesemiconductor elements 101, 102 are bonded to the surface 103 a of thefirst lead member 103 through the first soldering members 104. Next, theheat sinks 105 are respectively bonded to the first and secondsemiconductor elements 101, 102, also through the first solderingmembers 104. This state is shown in FIG. 14A. These integrated membersare referred to as a work 150.

Next, the surface 107 a of the second lead member 107 is bonded to thesemiconductor elements 101, 102 to which the heat sinks 105 are bonded,through the second soldering members 106 having a lower fusing point.Specifically, as shown in FIG. 14B, the second lead member 107 isdisposed on a jig 160 with the surface 107 a facing upward, and thesecond soldering members 106 are disposed on predetermined positions ofthe surface 107 a. Then, the work 150 shown in FIG. 14A is turned over,and disposed on the surface 107 a of the second lead member 107 throughthe second soldering members 106.

Further, a plate-shaped weight 161 made of stainless or the like is puton the other surface 103 b of the first lead member 103. The jig 160 isequipped with a spacer 162 having a specific height (for example, 1 mm)made of carbon or the like for determining the gap between the two leadmembers 103, 107. This state is shown in FIG. 14B. Then, the members areput in a heating furnace in this state, and only the second solderingmembers 106 undergo reflow.

Accordingly, the work 150 is pressurized by the weight 161, and as shownin FIG. 14C, the second soldering members 106 are crushed and the gapbetween the two lead members 103, 107 is decreased to the height of thespacer 162. Accordingly, the degree of parallelization between the twolead members 103, 107 is controlled. Incidentally, when the fusingpoints of the first soldering members 104 and the second solderingmembers 106 are respectively 320° C. and 240° C., a reflow temperatureis 250° C., and a load imparted from the weight 161 to the work 150 is0.08 g/mm² in this embodiment.

The thickness of the second soldering members 106 is preferably about100 μm to 300 μm. When it is too thin, the thickness for controlling thedegree of parallelization between the two lead members 103, 107 becomesinsufficient. When it is too thick, the thermal conductivity between thesemiconductor elements and the lead members becomes insufficient.Further, the second soldering members 106 containing Sn at 90 wt % ormore is advantageous to secure a sufficient thermal conductivity.Incidentally, after that, wire bonding with the outer lead 108 and resinmolding are performed. As a result, the semiconductor device shown inFIG. 13 is completed.

According to the manufacturing method described above, in the work 150in which the both surfaces of the semiconductor elements 101, 102 aresandwiched by the first and second lead members (radiation members) 103,107 through the first and second soldering members 104, 106, because thesecond soldering members 106 has a fusing point lower than that of thefirst soldering members 104, reflow can be performed only to the secondsoldering members 106.

Then, in this state, pressure is applied from the upper side of thefirst lead member 103 (or second lead member 107), so that the secondsoldering members 106 are deformed in the sate where the semiconductorelements 101, 102 are supported by the first soldering members 104.Accordingly, the degree of parallelization between the two lead members103, 107 can be controlled. For example, the degree of parallelizationbetween the two lead members 103, 107 can be made equal to or less than0.1 mm.

Thus, according to the present embodiment, the semiconductor devicehaving an appropriate degree of parallelization between the two members103, 107 can be provided. In FIG. 13, the semiconductor device candispense with the mold resin 10. In such a case, the degree ofparallelization between the two members 103, 107 can be controlledeasily.

Also, as shown in FIG. 15, the second lead member 107 can have recessportions 107 c (for example, having a depth of about 0.1 mm) on thesurface 107 a, and the second soldering members 106 can be disposed inthe recess portions 107 c. In this case, even when the second solderingmembers 106 are crushed during the reflow and pressurization so as toextrude, the recess portions 107 c prevent the soldering members 106from bulging out. Further, when the soldering members 106 are composedof soldering foils, the positioning becomes easy.

The second lead member 107 may be bonded to the semiconductor elements101, 102 through the second soldering members 106 without the heat sinks105. The present embodiment relates to the semiconductor device in whichthe semiconductor element is sandwiched by the pair of conductivemembers through the soldering members, and the conductive members mayhave only one of a radiation function and an electrode function.

(Eleventh Embodiment)

In an eleventh preferred embodiment, the present invention is applied toa semiconductor device as an electronic instrument shown in FIG. 16. Thesemiconductor device is, as shown in FIG. 16, composed of a heatingelement 201 and a pair of radiation members 202, 203 for radiating heatfrom the heating element 201. On a surface 201 a of the heating element201, a first side radiation member 202 is bonded through a radiationblock 204 and a bonding member 205, while on the other surface 201 b ofthe heating element 201, a second side radiation member 203 is bondedthrough a bonding member 205. That is, the radiation members 202, 203sandwich the semiconductor element 201 through the bonding members 205.

In this embodiment, the heating element 201 is a power semiconductorelement such as an IGBT or a thyrister. The bonding members 205 are madeof solder. The first side and second side radiation members 202, 203,and the radiation block 204 are made of Cu. Each plane shape of themembers 201 to 204 is generally rectangular.

Next, a method for manufacturing the semiconductor device is explained.First, the semiconductor element 201, the first side and second sideradiation members 202, 203, and the radiation block 204 are prepared.Each of the first side and second side radiation members 202, 203 has anarea in a plane direction larger than those of the semiconductor element201 and the radiation block 204.

Then, after solder paste is coated to the vicinity of the center on thesurface 203 a of the second side radiation member 203, the semiconductorelement 201 is disposed thereon. Then, likewise, semiconductor paste iscoated on the semiconductor element 201, and the radiation block 204 isdisposed thereon. Solder paste is further coated on the radiation block204.

Next, as shown in FIG. 16, a jig 206 for fixing the distance between thefirst side and second side radiation members 202, 203 is prepared. Thejig 206 has a pair of surfaces (parallel surfaces) 206 a, 206 b parallelwith each other. The jig 206 is so disposed on the second side radiationmember 203 that the surface 6 a contacts the surface 203 a of the secondside radiation member 203 where the semiconductor element 201 is notdisposed. Here, the jig 206 is made of a material such as Al, having athermal expansion coefficient larger than that of the first side andsecond side radiation members 202, 203 made of Cu.

Then, the first side radiation member 202 is disposed on the solderpaste applied to the radiation block 204 and on the surface 206 b of thejig 206, and a load is applied from the upper surface 202 b of the firstside radiation member 202 by, for example, a weight 208 as required.Accordingly, the first side radiation member 202 is externallypressurized so that the surface 202 a of the first side radiation member202 abuts the jig 206.

After that, the members 201 to 204 laminated as above undergo reflow inthis state, so that the solder paste is hardened to be solder 205, andthe semiconductor element 201, the radiation block 204, and the firstside and second side radiation members 202, 203 are bonded together.Successively, the weight 208 is removed, and the jig 206 is removed bypulling it in the lateral direction. As a result, the semiconductordevice in the present embodiment is completed.

According to the present embodiment, the distance between the surfaces(inner surfaces) 202 a, 203 a of the first side and second sideradiation members 202, 203 facing the semiconductor chip 201 can becontrolled by the thickness of the jig 206. As a result, when themembers 201 to 204 are assembled with each other by lamination, there isno need to consider dimensional tolerances of the first side and secondside radiation members 202, 203. Therefore, there is no need to thickenthe solder 205 to absorb the dimensional tolerances of the first sideand second side radiation members 202, 203. In consequence, thesemiconductor device can be provided with a solder thickness decreasedas small as possible.

Besides, in general, the respective members expand by heating during thereflow, and contract by cooling. The change in shape caused by thisexpansion and contraction becomes large as the thermal expansioncoefficient becomes large. In this embodiment, because the thermalexpansion coefficient of the jig 206 is large as compared to those ofthe first side and second side radiation members 202, 203 and theradiation block 204, after the members 201 to 204 are bonded together bythe solder 205 hardened in the sate where the respective members 201 to204 expand at the reflow, the jig 206 contracts much more than the othermembers 201 to 204 when returned to a room temperature.

As a result, the gap between the surfaces 202 a, 203 a of the first sideand second side radiation members 202, 203 becomes larger than thatbetween the parallel surfaces 206 a, 206 b of the jig 206. Because ofthis, the jig 206 can be detached readily. Also, because the degree ofparallelization between the first side and second side radiation members202, 203 can be controlled by the parallel surfaces 206 a, 206 b of thejig 206, the degree of parallelization between the first side and secondside radiation members 202, 203 can be secured even when the thicknessof the solder 205 is reduced.

Although the present embodiment exemplifies the case where the thermalexpansion coefficient of the jig 206 is larger that those of the othermembers 202 to 204, if the jig 206 can be detached after the members 201to 204 are bonded together, the jig 206 is not limited in the thermalexpansion coefficient. The shape of the jig 206 is not limited to thatshown in the figure, but may be other shapes so long as the jig 206 candetermine the distance between the first side and second side radiationmembers 202, 203.

The solder 205 is used as the bonding member, and is formed by hardeningsolder paste at reflow. However, the bonding may be performed byinterposing solder sheets between laminated members, and fusing andhardening the solder sheets. Conductive adhesive may be usedalternatively. The order of disposals of the semiconductor element 201,the radiation block 204, solder paste, and the jig 206 on the secondside radiation member 203 are not limited to that described above, andis changeable provided that the constitution shown in the figure can beobtained. It is described that the jig 206 has the parallel surfaces 206a, 206 b; however, the surfaces 206 a, 206 b need not be always parallelto each other provided that the jig 206 can fix the distance between thesurface 202 a of the first side radiation member 202 and the surface 203a of the second side radiation member 203. For example, the jig 206 canhave at least three protrusions at portions contacting the first sideand second side radiation members 202, 203.

Also, although it is not shown, in a case where a pad formed on thesurface of the semiconductor element 201 is wire-bonded to a lead frame,for example, the wire bonding can be performed after the jig 206 isdetached from the members bonded together. In this case, if thesemiconductor element 201 is disposed in the vicinity of the edgeportion of the second side radiation member 203, there is a case wherethe wire-bonding can be performed easily; however, the shape of thesecond side radiation member 203 can be modified appropriately so thatthe wire bonding to the pad becomes easier.

Further, the following method can be considered. Specifically, after thepad of the semiconductor element 201 is wire bonded to the lead frame bya wire, the jig 206 is disposed on the first side radiation member toavoid the wire and the lead frame, and then the second side radiationmember is disposed. In this state, the members 201 to 204 can be bonded.The semiconductor device in this embodiment may be sealed with resin.Also, the radiation members 202 to 204 may be made of ceramic substrateshaving metallized surfaces.

(Twelfth Embodiment)

FIG. 17 schematically shows a method for manufacturing a semiconductordevice in a twelfth preferred embodiment. This embodiment issubstantially identical with the eleventh embodiment in the constitutionof the semiconductor device, but differs in the method for manufacturingthe semiconductor device. Specifically, the method for controlling thedimension between the surfaces 202 a, 203 a of the first side and secondside radiation members 202, 203 differs form that in the firstembodiment. The same parts as those in the eleventh embodiment areassigned to the same reference numerals.

In this embodiment, first, the first side and second side radiationmembers 202, 203, the radiation block 204, and the semiconductor element201 are prepared. The first side and second side radiation members 202,203 are formed with through holes 221, 231 penetrating in the thicknessdirection at the respective four corners on a plane. The through holes221, 231 receive first and second protruding portions 261, 271 describedbelow.

Further, first and second jigs 260, 270 are prepared. The jigs 260, 270respectively have rectangular plate portions, and in the first jig 260,four first protruding portions 261 protrude from a surface 260 a of theplate portion, and in the second jig 270, four second protrudingportions 271 protrude from a surface 270 a of the plate portion. Thefirst and second protruding portions 261, 271 are provided approximatelysymmetrically, at inner portions than edge portions of the plateportions.

At the respective edge portions of the jigs 260, 270, protrudingportions 262, 272 for positioning respectively protrude from thesurfaces 260 a, 270 a for determining the distance between the first jig260 and the second jig 270. The protruding portions 261, 262, 271, 272have front end portions 261 a, 262 a, 271 a, 272 a each of which is agenerally flat face. The first and second jigs 260, 270 are made of, forexample, C (carbon).

Next, the surface 202 a of first side radiation member 202 is disposedon the surface 201 a of the semiconductor device 201 through theradiation block 204 and solder paste. On the other surface 201 b of thesemiconductor element 201, the second side radiation member 203 isdisposed at the side of the surface 203 a, through solder paste. Thatis, similarly to the eleventh embodiment, the second side radiationmember 203, the semiconductor element 201, and the radiation block 204are mounted through soldering paste, and the first side radiation member202 is further mounted on the radiation block 204 through solder pasteapplied.

Then, the first jig 260 is disposed with the surface 260 a facingupward, and a spring member 290 composed of a coil spring and arectangular base 291 bonded to the end of the coil spring is disposed onthe surface 260 a. The other end of the coil spring 290 may be bonded tothe surface 260 a of the first jig 260, and may not be bonded thereto.

Then, the laminated members 201 to 204 are disposed on the first jig 260so that the surface 203 b of the second side radiation member 203 issupported by the base 290 of the coil spring 290 disposed on the surface260 a of the jig 260 and so that the first protruding portions 261 areinserted into the holes 231 formed in the second side radiation member203. Then, the weight 208 is put on the surface 202 b of the first sideradiation member 202. The second jig 270 is positioned with the surface270 a facing downward, is approached to the surface 202 b of the firstside radiation member 202, and is installed so that the secondprotruding portions 271 are inserted into the holes 221 formed in thefirst side radiation member 202. Thus, the first side and second sideradiation members 202, 203, the radiation block 204, and thesemiconductor element 201 laminated as above are sandwiched by the firstand second jigs 260, 270.

Successively, the front end portions 262 a of the protruding portions262 formed on the first jig 260 for positioning are made abut the frontend portions 272 a of the protruding portions 272 formed on the secondjig 270 for positioning. Accordingly, a specific distance between thefirst and second jigs 260, 270 can be kept. That is, the distancebecomes the sum of the lengths of the protruding portions 262, 272.

At that time, the front end portions 261 a of the first protrudingportions 261 abut the surface 202 a of the first side radiation member202, and the front end portions 271 a of the second protruding portions271 abut the surface 203 a of the second side radiation member 203.Further, the first side and second side radiation members 202, 203 arepressurized from the surfaces 202 a, 203 a by the elastic force of thespring member 290 and the gravitational force of the weight 208.

Then, in the state where the respective members 201 to 204 are fixed bythe first and second jigs 260, 270, solder is hardened by reflow, andthe first side and second side radiation members 202, 203, the radiationblock 204, and the semiconductor element 201 are bonded together throughthe solder 205. After that, the first jig 260 and the second jig 270 arepulled in upper and lower direction so that the members 201 to 204bonded together can be detached from the jigs 260, 270. Thus, thesemiconductor device is completed.

According to the present embodiment, the protruding portions 261, 271can respectively be made abut the surfaces 202 a, 203 a of the firstside and second side radiation members 202, 203 while keeping a constantdistance between the first and second jigs 260, 270. Accordingly, thedistance between the surfaces 202 a, 203 a of the first side and secondside radiation members 202, 203 can be controlled. That is, referring toFIG. 17, the overlapping length K of the first and second protrudingportions 261, 271 is kept constant. Also, the surfaces 202 a, 203 a ofthe first side and second side radiation members 202, 203 arerespectively supported by the four first protruding portions 261, andthe four second protruding portions 271. Therefore, the degree ofparallelization between the first side and second side radiation members202, 203 can be secured by controlling the lengths of the protrudingportions 261, 271.

Therefore, there are no need to consider the dimensional tolerances ofthe first side and second side radiation members 202, 203, and no needto thicken the solder 205 for absorbing the dimensional tolerances ofthe first side and second side radiation members 202, 203. Themanufacturing method in this embodiment can provide a semiconductordevice in which the solder thickness is reduced as thin as possible.

Also, because the holes 221, 231 are formed in the first side and secondside radiation members 202, 203, the front end portions 261 a, 271 a ofthe first and second protruding portions 261, 271 suitably abut thesurfaces 202 a, 203 a of the first side and second side radiationmembers 202, 203 by penetrating the holes 231, 221. The insertions ofthe first and second protruding portions 261, 271 into the holes 231,221 formed in the second side and first side radiation members 203, 202can position the first side and second side radiation members 202, 203in the horizontal direction, i.e., the direction parallel to thesurfaces 202 a, 203 a.

Because the second side radiation member 203 is held by the springmember 290, the second side radiation member 203 can be suitablypressurized by the elasticity of the spring member 290 even when thedimensional error of the second side radiation member 203 is large. Inaddition, because the first side radiation member 202 is pressurized bythe movable weight 208, the first side radiation member 202 can besuitably pressurized even when the dimensional error of the first sideradiation member 202 is large.

Even when the radiation members 202, 203 are different from each otherin thickness, the same jigs 260, 270 as described above can be usedbecause the pressurization can be controlled by the spring member 290and the weight 208, and because of the same reasons as described aboveinvolving the employments of the spring member 290 and the weight 208.

More specifically, for example, in the sate shown in FIG. 17, it isassumed that solid members having high rigidity are disposed in the gapbetween the first side radiation member 202 and the second jig 270, andin the gap between the second side radiation member 203 and the firstjig 260 with heights corresponding to the gaps. In this case, if thethicknesses of the first side and second side radiation members 202, 203are too thick, stresses applied to the first side and second sideradiation members 202, 203 can be increased by interposing them betweenthe front end portions 261 a, 271 a of the protruding portions 261, 271and the solid members. This might result in breakage of the first sideand second side radiation members 202, 203. On the other hand, if thethicknesses of the first side and second side radiation members 202, 203are too thin, the front end portions 261 a, 271 a of the protrudingportions 261, 271 could not abut the respective radiation members 202,203. To the contrary, in this embodiment, the first side and second sideradiation members 202, 203 can be pressurized suitably by adopting thespring member 290 and the weight 208.

Also, because it is so constructed that the semiconductor device can bedetached from the jigs 260, 270 by detaching the jigs 260, 270respectively in the upper and lower directions, the detachment is easy.The jigs 260, 270 need not have plate-like shapes, and can have variousshapes as long as the first and second protruding portions 261, 271 areprovided. To support the surfaces 202 a, 203 a of the first side andsecond side radiation members 202, 203, it is sufficient to providethree protruding portions 261 or 271 for each. The front end portions261 a, 262 a, 271 a, 272 a of the protruding portions 261, 262, 271, 272may not be flat.

The protruding portions 262, 272 for positioning may not be provided onthe respective jigs 260, 270. For example, the second side radiationmember may be formed with a long protruding portion for positioning witha front end portion that abuts the surface 260 a of the jig 260, withoutforming the protruding portion for positioning on the first jig 260.Further, if an external apparatus or the like can fix the intervalbetween the jigs 260, 270, there is no need to provide the protrudingportions for positioning.

In the figure, only one semiconductor device is shown to bemanufactured; however, several semiconductor devices can be manufacturedat the same time by using first and second jigs having several pairs offirst and second protruding portions. Although the holes 221, 231 forreceiving the protruding portions 261, 271 are formed to penetrate thefirst side and second side radiation members 202, 203, notches notchedfrom the edge portions of the radiation members 202, 203 and allowingthe protruding portions 261, 271 to penetrate therein may be formed inplace of the holes 221, 231.

Otherwise, for example, the first protruding portions 261 can passthrough the outside of the second side radiation member 203 bydecreasing the area of the second side radiation member 203. In thiscase, the holes 231 are not formed in the second side radiation member203. The first side radiation member 202 has the through holes 221 forallowing the second protruding portions 271 to be inserted therein.

Otherwise, the respective radiation members 202, 203 may be warped orbent at edge portions so that the protruding portions 261, 271 can passthrough with the front end portions 261 a of the first protrudingportions 261 abutting the surface 202 a of the first side radiationmember 202, and the front end portions 271 a of the second protrudingportions 271 abutting the surface 203 a of the second side radiationmember 203.

Although the weight 208 is disposed on the first side radiation member202, the spring member 290 may be disposed between the surface 202 b ofthe first side radiation member 202 and the surface 270 a of the secondjig 270. Although the spring member 90 is composed of a coil spring inthis embodiment, it may be composed of other elastic members. Further,the front end portions 261 a, 271 a of the first and second protrudingportions 261, 271 may be brought in contact with the radiation members202, 203 when the reflow is performed to bond the members 201 to 204, byadopting a thermally deformable member such as a shape memory alloy,bimetal, or the like that deforms during the reflow.

As shown in FIG. 18, dispensing with the weight 208, the second jig 270may be formed with a through hole 273 extending in the thicknessdirection. In this case, after the laminated members are sandwiched bythe first and second jigs 260, 270, a member 281 for pressurization canbe inserted into the through hole 273 from the side of the surface 270 bof the jig 270, and pressurize the surface 202 b of the first sideradiation member 202.

Here, another method for manufacturing the semiconductor device in thisembodiment is explained. In the method described above, after therespective members 201 to 204 are laminated using solder paste, they aresandwiched by the first and second jigs 260, 270. However, after thelaminated members 201 to 204 undergo reflow to be bonded by solder 205,the bonded members may be sandwiched by the first and second jigs 260,270 and undergo the reflow again. At that time, the solder hardened isfused or softened to allow the members 201 to 204 to move, and themembers 201 to 204 can be rearranged according to the dimensionsdetermined by the jigs 260, 270. In this state, the solder 205 ishardened again.

Alternatively, the state shown in FIG. 17 can be provided by disposingthe spring member 290, the base 291, the second side radiation member203, a solder sheet, the semiconductor element 201, a solder sheet, theradiation block 204, a solder sheet, the first side radiation member202, the weight 208, and the second jig 270, on the first jig 260 inthis order, and by performing reflow to fuse and harden the soldersheets and to bond the members 201 to 204 together.

(Thirteenth Embodiment)

Hereinafter, a thirteenth preferred embodiment of the present inventionis explained with reference to FIG. 19. Semiconductor chips used in thisembodiment are a semiconductor chip in which an IGBT is formed (IGBTchip) 301 and a semiconductor chip in which a FWD (fly-wheel diode) isformed (FWD chip) 302. The semiconductor chips 301, 302 are made ofmainly Si and have a thickness of about 0.5 mm. In the semiconductorchips 301, 302, element formation surfaces are referred to as mainsurfaces 301 a, 302 a, and the opposite surfaces are referred to as backsurfaces 301 b, 302 b. An emitter electrode is formed on the mainsurface 301 a of the IGBT chip 301 and a collector electrode is formedon the back surface 301 b of the IGBT chip 301, though they are notshown.

To the main surfaces 301 a, 302 a of the semiconductor chips 301, 302,back surfaces 303 b of heat sinks (E heat sinks) 303 as first conductivemembers are bonded through solder 304 as first bonding members havingelectrical conductivity. In the E heat sinks 303, a bonding area betweenthe IGBT chip 301 and the E heat sink 303 is approximately the same asthe area of the emitter electrode of the IGBT chip 301. Accordingly, theE heat sink 303 can contact the emitter electrode at the area as largeas possible, and be prevented from contacting a peripheral portion ofthe emitter electrode.

On the main surface 301 a of the IGBT chip 301, there exists a regionsuch as a guard ring that might have a problem when it is madeequipotential with the emitter electrode. If the heat sink 303 contactsthis region, the region would have the same potential as that of theemitter electrode through the heat sink 303. Therefore, the contact areaof the IGBT 301 and the E heat sink 303 is set to be approximately equalto the area of the emitter electrode of the IGBT chip 301. Accordingly,the E heat sink 303 can be bonded to the IGBT chip 301 without causingany problems.

To the back surfaces 301 b, 302 b of the semiconductor chips 301, 302, amain surface 305 a of a second conductive member 305 is bonded(electrically connected) through solder 304 as second bonding members.To main surfaces 303 a of the heat sinks 303 at an opposite side of theback surfaces 303 b, a back surface 306 b of a third conductive member306 is bonded (electrically connected) through solder 304 as thirdbonding members.

The E heat sinks 303, and the second and third conductive members 305,306 can be made of metallic members having electrical conductivity. Inthis embodiment, the E heat sinks 303 are made of Cu, and the second andthird conductive members 305, 306 are made of Cu alloy. The second andthird conductive members 305, 306 are plate-shaped members. The E heatsinks 303 also are plate-shaped members, but have step portions 303 c asdescribed below.

Each of the E heat sinks 303 is formed to protrude toward the thirdconductive member 306 by the step portion 303 c, and has a thin portion303 d at the side of the semiconductor chips 301, 302. The thin portion303 d is thinned in the thickness direction of the semiconductor chip301. Accordingly, in each of the E heat sinks 303, the bonding areabetween the E heat sink 303 and the third conductive member 6 is smallerthan that between the E-heat sink 303 and the semiconductor chip 301 or302.

Besides, a surface treatment such as Ni plating is performed to thesurface portions of the E heat sinks 303 where it is bonded to therespective semiconductor chips 301, 302 and the third conductive members306 to improve wettability of the solder 304. The other outer surfacesof the E heat sinks 303 for contacting a sealing member described beloware oxidized. The second and third conductive members 305, 306 areplated with Ni at entire outer surfaces thereof. In the second and thirdconductive members 305, 306 and the E heat sinks 303, the thickness ofthe thickest portion is about 1 mm, and the thickness of the thinportion is about 0.4 mm.

A land (not shown) is formed on the main surface of the IGBT chip 301,and is electrically connected to a control terminal 307 of a lead framevia a bonding wire 308. Then, the semiconductor chips 301, 302, the Eheat sinks 303, the main surface 305 a of the second conductive member305, the back surface 306 b of the third conductive member 306, and apart of the control terminal 307 are integrally sealed with resin 309 asa sealing member. Used as the resin 309 is, for example, epoxy basedmold resin. Accordingly, a the members 301 to 308 are integrally sealedto have the back surface 305 b of the second conductive member 305, themain surface 306 a of the third conductive member 306, and a part of thecontrol terminal 307 that are exposed from the resin 9.

Thus, the semiconductor device in this embodiment is constructed. Inthis semiconductor device, heat generated from the semiconductor chips301, 302 is transferred to the E heat sinks 303, and to the second andthird conductive members 305, 306 through the solder 304, and then isradiated from the back surface 305 b of the second conductive member 305and the main surface 306 a of the third conductive member 306.

When cooling members or the like are disposed to abut the back surface305 b of the second conductive member 305 and the main surface 306 a ofthe third conductive member 306, heat radiation can be furtherfacilitated. Here, the E heat sinks 303 and the second and thirdconductive members 305, 306 form electrical paths for the respectivesemiconductor chips 301, 302. That is, the electrical communication withthe collector electrode of the IGBT chip 301 is provided through thesecond conductive member 305, while the electrical communication withthe emitter electrode of the IGBT chip 301 is provided through thesecond conductive member 306 and the E heat sink 303.

As explained above, in the present embodiment, each of the E heat sinks303 bonded to the surfaces 301 a, 302 a of the semiconductor chips 301,302 has the step portion 303 c and accordingly has the thin portion 303d. Because the thin portion 303 d has small rigidity, the thin portion303 d can follow deformation of the resin 309 surrounding it and canabsorb thermal stress when the semiconductor device undergoes thermalcycle. Therefore, stress concentration on the solder 304 bonding thesemiconductor chips 301, 302, and the E heat sinks 303 can be mitigated.

In general, the smaller the bonding area of solder is, the smaller thebonding strength of the solder becomes. Therefore, in each of the E heatsinks 303, the bonding area with the third conductive member 306 is setto be smaller than that with the semiconductor chip 301 or 302.Accordingly, cracks become liable to be produced in the solder 304bonding the E heat sink 303 and the third conductive member 306.

As a result, when thermal stress is increased, cracks are produced firstin the solder 304 bonding the E heat sink 303 and the third conductivemember 306 to mitigate thermal stress, and accordingly thermal stressapplied to the solder 304 bonding the E heat sink 303 and thesemiconductor chip 301 or 302 can be lessened.

Incidentally, even when cracks are produced in the solder 304 bondingthe E heat sink 303 and the third conductive member 306 as a result ofstress concentration, because both the E heat sink 303 and the thirdconductive member 306 include Cu as a main component, those deformationscaused by the thermal cycle are approximated to each other and cracks donot advance largely in the solder 304. Even if the cracks advance,because the current path is formed by the entire bonding surface betweenthe E heat sink 303 and the third conductive member 306, significantproblems do not occur.

Further, because the surface portions of the E-heat sink 303 forcontacting the resin 309 are oxidized, adhesion with the resin 309 canbe improved. As a result, the deformation of the resin 309 caused bythermal stress and the deformation of the E heat sink 303 synchronizewith each other, and stress concentration on the solder 304 bonding theE heat sink 303 and the semiconductor chip 301 or 302 can be mitigated.Incidentally, adhesion between Cu alloy and the resin 309 is improved byplating the Cu alloy with Ni. Therefore, the surfaces of the second andthird conductive members 305, 306 are plated with Ni instead ofoxidation.

Thus, thermal stress concentration to the solder 304 bonding therespective semiconductor chips 301, 302 and the E heat sinks 303 can besuppressed, so that cracks can be prevented to reach this solder 304.Even when several cells are formed on the main surface (elementformation surface) 301 a of the IGBT chip 301, current is prevented fromconcentrating on a cell provided at the center, and breakage of the cellis prevented.

Also, because each of the E heat sinks 303 has the step portion 303 c,as compared with a case of adopting a prism shape heat sink without astep portion, a creepage distance from the interface between the thirdconductive member 306 and the resin 309 to the bonding portion betweenthe semiconductor chip 301 or 302 and the E heat sink 303 is long.Because of this, it can be retarded that cracks produced at theinterface between the third conductive member 306 and the resin 309reach the bonding portion between the semiconductor chip and the E heatsink 303.

With respect to the semiconductor device according to this embodiment, athermal shock cycle test was performed, in which the semiconductordevice was exposed to environments of −40° C. and 125° C. respectivelyfor 60 minutes, a resistance between the third conductive member 306 andthe control terminal 307 was measured, and a rate of change inresistance was calculated using an initial value as a reference. Then,it was confirmed that the rate of change in resistance did not increaselargely even at 200 cycles. It was further confirmed that the rate inchange of resistance of the semiconductor device in this embodiment wassmall as compared to a case where the heat sink had no step portion.

Next, a method for manufacturing the semiconductor device in thisembodiment is explained with reference to FIGS. 20A to 20C. First, thesecond and third conductive members 305, 306 are formed from plates madeof cupper alloy or the like by punching. After that, the entire outersurfaces of the second and third conductive members 305, 306 are platedwith Ni.

Cu plates are prepared for forming the E heat sinks 303. Ni plating isperformed to both the main and back surfaces of each Cu plate. Afterthat, Cu members having a size corresponding to the E heat sinks 303 areformed from the Cu plates plated with Ni, by punching or the like. Then,each of the Cu members is pressed to have the step portion 303 c. Thus,the E heat sinks 303 are completed. Each of the E heat sinks 303 hasportions plated with Ni for being bonded to the semiconductor chip 301or 302 and to the third conductive member 306, and portions exposed bypunching and not plated with Ni. At the exposed portions, plating ispeeled off by pressing.

As shown in FIG. 20A, the semiconductor chips 301, 302 are bonded to themain surface 305 a of the second conductive member 305 through thesolder 304. Next, the E heat sinks 303 are bonded to the respectivesemiconductor chips 301, 302 through the solder 304. The solder 304 usedfor bonding the semiconductor chips 301, 302 and the second conductivemember 305, and the E heat sinks 303 has a relatively high fusing point.For example, solder composed of 10 wt % Sn (tin) and 90 wt % Pb (lead)and having a fusing point of 320° C. (high temperature solder) can beused as the solder 304. Accordingly, the state shown in FIG. 20A isprovided, which is referred to as a work 310.

Next, as shown in FIG. 20B, the third conductive member 306 is put on ajig 311 with the back surface 306 b facing upward, and solder 4 isdisposed on desirable regions of the back surface 306 b. Then, the work310 shown in FIG. 20A is turned over, and is disposed on the thirdconductive member 306. The solder 4 interposed between the thirdconductive member 306 and the semiconductor chips 301, 302 has a fusingpoint lower than that of the high temperature solder described above.For example, solder containing Sn at 90 wt % or more and having a fusingpoint of 240° C. can be used as the solder 4. Hereinafter, this solderis referred to as low temperature solder.

Further, a plate-shaped weight 312 is disposed on the back surface 305 bof the second conductive member 305. Here, the jig 311 has a spacer 313having a predetermined height for fixing the distance between the secondand third conductive members 305, 306. This state is shown in FIG. 20C.In this state, it is put into a heating furnace, and reflow is performedonly to the low temperature solder 4. As a result, the work 310 ispressurized by the weight 312, and as shown in FIG. 20C, the lowtemperature solder 4 is crushed so that the distance between the backsurface 306 b of the third conductive member 306 and the main surface305 a of the second conductive member 305 corresponds to the height ofthe spacer 313. Accordingly, the degree of parallelization between thesecond and third conductive members 305, 306 can be adjusted.

Also, the E heat sinks 303 are bonded to the respective semiconductorchips 301, 302 in the state where the E heat sink 303 contacts only theemitter electrode on the IGBT chip 301 by the high temperature solder304, and are bonded to the third conductive member 306 by the lowtemperature solder 304. Therefore, when the heat sinks 303 are bonded tothe third conductive member 306, the high temperature solder 304 doesnot fuse, and the bonding positions of the E heat sinks 303 to thesemiconductor chips 301, 302 can be appropriately maintained.Incidentally, when the fusing points of the high temperature solder 304and the low temperature solder 304 are respectively 320° C. and 240° C.,the reflow temperature for the low temperature solder 304 is preferably250° C.

After that, although it is not shown, the control terminal 307 and theIGBT chip 301 are electrically connected to each other by the bondingwire 308, and the members 301 to 308 are sealed with resin 309 as shownin FIG. 19. This resin sealing is performed by injecting the resin 309having a temperature of about 180° C. into spaces provided among themembers 301 to 308. At that time, the surface portions of the E heatsinks 303 exposing copper and not bonded to either of the semiconductorchips 301, 302 and the third conductive member 306 are oxidized. Thus,the semiconductor device is completed.

In general, when Ni plating is performed to the E heat sink, after the Eheat sink is formed into the shape capable of being disposed between thesemiconductor chip and the third conductive member, the E heat sink isput in a plating machine, and an entire area of the outer surface of theE heat sink is plated. Therefore, the solder disposed on the E heat sinkcan easily wet and expand to the region other than the bonding portionswith the semiconductor chip and the third conductive member.

In addition, the thickness of the E heat sink 303 is thin, i.e., about 1mm, the low temperature solder 304 and the high temperature solder 304are located at close positions to each other. If the Ni plating isperformed to the entire outer surface of the E heat sink 303, therearises a case where the low temperature solder 304 and the hightemperature solder 305 are mixed with each other. As a result, eutecticsolder having a fusing point much lower than that of the low temperaturesolder 304 might be formed, which can fuse at the temperature (forexample, 180° C.) for sealing the members 301 to 308 with the resin 309.

As opposed to this, in the present embodiment, Ni plating is performedonly to the portions of the E heat sink 303 for bonding thesemiconductor chip 301 or 302 and the third conductive member 306. Thelow temperature solder 304 and the high temperature solder 304 aredisposed with the oxide surface of Cu interposed therebetween. Becausethe wettability of the oxide surface of Cu to the solder 304 is low, thehigh temperature solder 304 and the low temperature solder 304 do notexpand to other regions than the bonding portions, and do not mix witheach other. Incidentally, although solder is used as the bonding members(first to third bonding members) in this embodiment, Ag paste or thelike can be used alternatively. The bonding members need not be alwaysan identical material with one another.

(Fourteenth Embodiment)

FIG. 21 shows a semiconductor device in a fourteenth preferredembodiment. The fourteenth embodiment differs from the thirteenthembodiment in the shape of the third conductive member 306. Hereinafter,different portions from the thirteenth embodiment are mainly explained.In FIG. 21, the same parts as those in FIG. 19 are assigned to the samereference numerals, and the same explanations are not reiterated.

As shown in FIG. 21, a step portion 306 c is formed on the main surface306 a of the third conductive member 306. Then, the step portion 306 cis covered with the resin 309 for sealing. Accordingly, creepagedistances from the interface between the resin 309 and the thirdconductive member 306 to the bonding portions of the E heat sinks 303with the semiconductor chips 301, 302 on the surface of thesemiconductor device can be further increased as compared to those inthe first embodiment. As a result, cracks are further suppressed frombeing produced in the solder 4 bonding the semiconductor chips 301, 302and the E heat sinks 303.

Incidentally, the creepage distances can be further increased as thearea covered with the resin 309 on the surface 306 a of the thirdconductive member 306 is increased. However, the decreased exposed areaof the third conductive member 306 deteriorates the radiation property.Therefore, the third conductive member 306 should be covered with theresin 309 at a degree not to deteriorate the radiation property.

(Fifteenth Embodiment)

FIG. 22 shows a semiconductor device in a fifteenth preferredembodiment. This embodiment differs from the thirteenth embodiment in apoint that conductive members are disposed between the respectivesemiconductor chips 301, 302 and the second conductive member 305.Hereinafter, portions different from the thirteenth embodiment aremainly described. In FIG. 22, the same parts as those in FIG. 19 areassigned to the same reference numerals.

As shown in FIG. 22, collector heat sinks (C heat sinks) 314 aredisposed between the second conductive member 305 and the respectivesemiconductor chips 301, 302, at the side of the back surfaces 301 b,302 b of the semiconductor chips 301, 302. The C heat sinks 314 hasareas approximately the same as those of the corresponding semiconductorchips 301, 302 in a direction perpendicular to the thickness directionof the semiconductor chips 301, 302.

Specifically, surfaces (main surfaces) 314 a of the C heat sinks 314 arerespectively bonded to the back surfaces 301 b, 302 b of thesemiconductor chips 301, 302 through the solder 304. Back surfaces 314 bof the C heat sinks 314 are bonded to the main surface 305 a of thesecond conductive members 305 through the solder 304.

The second conductive member 305 has a relatively large area withrespect to its thickness, and therefore has a possibility that it isbent (warped). On the other hand, when the injection of the resin 309 isperformed, the back surface 305 b of the second conductive member 305and the main surface 306 a of the third conductive member 306 arepinched under relatively large pressure to prevent leakage of the resin309. Therefore, if the second conductive member 305 holding thesemiconductor chips 301, 302 is bent, the pressure pinching the secondand third conductive members 305, 306 during the sealing canmechanically cause damages to the semiconductor chips 301, 302.

As opposed to this, in this embodiment, the C heat sinks 314 aredisposed on the back surfaces 301 b, 302 b of the semiconductor chips301, 302, and the C heat sinks 314 are smaller than the secondconductive member 305 in size. Therefore, the bending can be suppressedand the semiconductor chips 301, 302 can be securely prevented frombeing damaged. Thus, this embodiment can prevent the mechanical damageto the semiconductor chips 301, 302, in addition to the effects asattained in the thirteenth embodiment. Incidentally, in the constitutiondescribed in the fourteenth embodiment in which the third conductivemember 306 has the step portion 306 c that is covered with the resin309, the C heat sinks 314 can be disposed as well.

In the thirteenth to fifteenth embodiments described above, the E heatsinks 303 respectively have the thin portions 303 d at the side of thesemiconductor chips 301, 302; however, as shown in FIG. 23, the stepportions 303 d may be provided at the side of the third conductivemember 306. Also in this constitution, thermal stress can be preventedfrom concentrating on the solder 4 at the bonding portions between thesemiconductor chips 301, 302 and the heat sinks 303 by the low rigiditythin portions 303 d that can absorb the thermal stress, as compared tothe case where the E heat sinks have a prism-like shape.

In the thirteenth to fifteenth embodiments described above, in each ofthe E heat sinks 303, the step portion 303 c is provided at an entireportion contacting the resin 309; however, with respect to the solder304 bonding the semiconductor chips 301, 302 and the E heat sinks 303,cracks progress from the periphery side of the resin 309 toward thecenter. Therefore, the step portion 303 c may be provided only at theportion facing the outer periphery of the resin 309. Here, the peripheryof the resin 309 means a periphery of a portion surrounding the secondand third conductive members 305, 306, and in FIG. 19 it corresponds asurface approximately parallel to the thickness direction of thesemiconductor chips 301, 302.

(Sixteenth Embodiment)

FIG. 24 shows a semiconductor device in a sixteenth preferredembodiment. In this embodiment, an IGBT 411 and a FWD (free-wheel diode)412 each of which is made of a Si substrate are used as semiconductorchips. At a side of each element formation surface (first surface) 401 aof the IGBT 411 and the FWD 412, first side and second side radiationmembers 421, 422 are bonded through solder 431. A third radiation member423 is further bonded to the first side and second side radiationmembers 421, 422 through solder 432 at an opposite side of the chips411, 412. The first to third radiation members 421 to 423 are made of,for example, Cu and constitute a first side radiation member 420.

The third radiation member 423 is a plate having a protruding portion423 b, and has a generally L-shape cross-section with the protrudingportion 423 b as a short side in a thickness direction thereof. Thefirst side and second side radiation members 421, 422 are bonded to along side of the L-shape of the third radiation member 423. Theprotruding portion 423 b has a front end portion 423 a that isapproximately coplanar with second surfaces 401 b of the chips 411, 412at an opposite side of the first surfaces 401 a.

Besides, a DBC (Direct Bonding Cupper) substrate 404 is disposed as ahigh thermal conductivity insulating substrate at a side of the secondsurfaces 401 b of the chips 411, 412. The DBC substrate 404 is composedof an AlN (aluminum nitride) substrate 405 both first and secondsurfaces 405 a, 405 b of which are patterned with copper foils 451 to454. The second surfaces 401 b of the chips 411, 412 are respectivelybonded to a first copper foil 451 on the first surface 405 a of the DBCsubstrate 404, through solder 433. Further, the front end portion 423 aof the protruding portion 423 b of the third radiation member 423 isbonded to the second copper foil 452 of the DBC substrate 404, throughsolder 434.

Next, the electrode (wiring) portion of the IGBT 411 is explained withreference to FIG. 25 showing a part surrounded by a broken line in FIG.24. As shown in FIG. 25, a barrier metal 111 is formed on a substrate100 of the IGBT 411 at the side of the first surface 401 a. An emitterelectrode 112 and a land 113 for wire bonding are further formed frompure Al. The barrier metal 111 is composed of Ti (titanium) and TiN(titanium nitride) which are formed on the substrate 100 at this order,and has a thickness of about 0.1 μm. The thickness of the electrode 112,113 is about 5 μm.

Further, a metallic film 114 is formed on the emitter electrode 112 tobe suitably connected with the solder 431. The metallic film 114 iscomposed of Ti, Ni (nickel), and Au (gold) formed from the side of theemitter electrode 112 sequentially, and has a total thickness of about0.6 μm. To this metallic film 114, as described above, the first sideradiation member 421 is bonded through the solder 431. Here, thethicknesses of the solder 431 and the first side radiation member 421are, for example, about 0.1 mm and about 1.5 mm respectively.

On the other hand, at the side of the second surface 401 b of thesubstrate 100, a collector electrode 115 made of pure Al is formedwithout barrier metal. The collector electrode 115 is, for example,about 0.2 μm in thickness. A metallic film 116 is then formed on thecollector electrode 115, similarly to the emitter electrode 112. Themetallic film 116 is bonded to the first cupper foil 451 on the firstsurface 405 a of the DBC substrate 404 through the solder 433.Incidentally, the electrode portion of the FWD 412 has a structuresubstantially the same as that of the IGBT 411.

Further, as shown in FIGS. 24 and 25, the third radiation member 423 iselectrically connected to a lead 461 by a connection terminal 406 a forelectrically connecting the emitter electrode 112 and the lead (emitterterminal) 461 as an outside terminal. On the DBC substrate 404, a land453 is formed, and is wire-bonded to the land 113 on the surface 401 aof the IGBT 411 by a wire 407. The land 453 of the DBC substrate 404 isfurther wire-bonded to a gate terminal 408 by another wire 407. As thewires 407, Au, Al, or the like used generally for wire bonding can beused. The land 453 of the DBC substrate 404 is provided for anintermediation between the land 113 and the gate terminal 308.

To the copper foil 454 formed on the back surface 405 b of the DBCsubstrate 404, a fourth radiation member (second side radiation member)424 is bonded through solder 435. That is, the first side radiationmember 420 and the second side radiation member 424 are joined togetherwith the DBC substrate 404 interposed therebetween, and electricalinsulation and electrical conductivity of the respective radiationmembers 420, 424 can be secured respectively.

Then, the members described above are sealed with resin 400 so that thefourth radiation member 424 has a radiation surface 409 exposed at anopposite side of the surface bonding the DBC substrate 404. For example,epoxy based mold resin can be used as the resin 400.

Next, the electrical connection in each part of the semiconductor devicein this embodiment is explained in more detail, referring to FIG. 26that shows the semiconductor device in a direction indicated by arrowXXVI in FIG. 24. Incidentally, FIG. 24 shows a cross-section taken alongline XXIV—XXIV in FIG. 26. The semiconductor device holds two pairs ofthe IGBT 411 and the FWD 412 in this embodiment.

The first side radiation member 420 (421 to 423) is indicated with aone-dot chain line in the figure, and as described above, iselectrically connected with the emitter terminal 461 through theconnection terminal 406 a. The first copper foil 451 of the DBCsubstrate 404 is bonded to all of the electrodes on the surfaces 401 bof the IGBTs 411 and the FWDs 412, and has a protruding portion 451 aprotruding not to contact the second cupper foil 452 of the DBCsubstrate 404. The protruding portion 451 a is electrically connected tothe collector terminal 462 as a lead through a connection terminal 406b.

In this semiconductor device, the radiation surface 409 is fixed to aradiation fin (not shown) as a cooling member (outside radiator) byscrewing or the like. Accordingly, heat generated from the firstsurfaces 401 a of the chips 411, 412 is radiated from the radiationsurface 409 through the first side radiation member 420, the DBCsubstrate 404, and the second side radiation member 424. That is, theradiation direction from the first surfaces 401 a of the chips 411, 412corresponds to the direction extending from the first surfaces 401 a tothe second surfaces 401 b in the respective chips 411, 412 (from theupper side to the lower side in FIG. 24).

On the other hand, heat generated from the second surfaces 401 b of thechips 411, 412 is also radiated from the radiation surface 409 throughthe DBC substrate 404 and the second side radiation member 424. Thus, inthe semiconductor device in which the chips are mounted, radiation ofheat from both the surfaces 401 a, 401 b of the chips 411, 412 isperformed mainly by the same radiation surface 409.

Next, a method for manufacturing the semiconductor device in thisembodiment is explained. First, as describe above, the IGBT 411 havingthe barrier metal 111, the emitter electrode 112, the collectorelectrode 115, the metallic films 114, 116, and the like and the FWD 412are prepared. The electrodes 112, 115, the barrier metal 111, themetallic films 114, 116, and the like are formed by sputtering or thelike. Then, the first side and second side radiation members 421, 422are soldered to the first surfaces 401 a of the chips 411, 412.

Next, the DBC substrate 404 having the first and second surfaces 405 a,405 b on which the cupper foils 451 to 454 are patterned is prepared,and the 411 and the FWD 412 are soldered to predetermined portions ofthe DBC substrate 404. After that, the third radiation member 423 issoldered not only to the first side and second side radiation members421, 422 but also to the DBC substrate 404. When soldering the thirdradiation members 423, a thickness of solder is thickened at the bondingportion with the DBC substrate 404 as compared to that with the firstside and second side radiation members 421, 422, and accordingly,variations in thickness by soldering is absorbed.

These soldering can be performed by reflow or the like. When kinds ofsolder used in this method are changed so that fusing points of soldersare decreased in the order of the soldering, the soldering can besufficiently performed without affecting the solder that has beensoldered first. Then, the emitter terminal 461 and the collectorterminal 462 are connected to the third radiation member 423, and theIGBT 411 and the gate terminal 408 are wire-bonded to each other.Successively, the fourth radiation member 424 is soldered to the DBCsubstrate 404, and finally resin sealing is performed.

According to the present embodiment, because an elastic modulus of pureAl is small, thermal stress produced due to differences among the chips411, 412 and the radiation members 421 to 424 can be mitigated.Specifically, the elastic modulus of pure Al is 72 GPa, and an elasticmodulus of Al containing Si at 1% is about 75 GPa. When the Alcontaining Si is used, Si may be segregated. In such a case, because theelastic modulus of Si is 130 GPa, the capability for mitigating thermalstress is locally but significantly decreased.

As opposed to this, in this embodiment, especially because the emitterelectrode 112 of the IGBT 411 is made of pure Al, stress is preventedfrom concentrating on the emitter cell, and fluctuation in electricalcharacteristics such as Vt can be suppressed. Therefore, the chip andthe semiconductor device can be provided with high electricalreliability. Also, because the electrodes on the second surfaces 401 bof the chips 411, 412 are made of pure Al, the chips 411, 412 areprevented from being warped due to thermal stress.

Also, because Si is not contained in the electrodes 112, 113, 115,deposition of Si nodule can be prevented. This is especially effectivefor the land 113 for wire bonding because Si nodule can cause cracks inthe device by vibrations (stress) produced by wire-bonding. Thus,externally applied stress can be mitigated by forming the electrodes112, 113, 115 from pure Al.

However, when the pure Al is brought in direct contact with thesubstrate 100 made of Si, ally spikes are produced. Therefore, thebarrier metal 111 is disposed between the electrodes 112, 113 and thesubstrate 100, and prevents the generation of alloy spikes.Incidentally, the barrier metal is not formed on the other surface 401 bof the IGBT 411. This is because even-when alloy spikes are produced onthe other surface 401 b, the alloy spikes do not reach the device formedat the side of the surface 401 a.

In the semiconductor device in which a chip is sandwiched by a pair ofradiation members respectively having radiation surfaces, coolingmembers sandwich the semiconductor device to contact the radiationsurfaces respectively. However, in this constitution, stress producedwhen the cooling members sandwiche the semiconductor device is liable tobe concentrate on the chip.

As opposed to this, in this embodiment, the radiation surface 409 forradiating heat to the outside of the semiconductor device is formed atone side (the side of the second surfaces 401 b) of the chips 411, 412.In this constitution, the semiconductor device needs not be sandwichedby the cooling members for radiating heat. Therefore, even when theradiation surface 409 is firmly bonded to the outside cooling member,large stress is not applied to the chips 411, 412.

Especially, because the radiation surface 409 is provided at the side ofthe second surfaces 401 b of the chips 411, 412, stress is preventedfrom concentrating on the first surfaces 401 a of the chips 411, 412,and the fluctuations in electric characteristics of the device providedat the first surface side can be securely prevented.

Further, because both surfaces 401 a, 401 b of the chips 411, 412 arebonded to the radiation members 421, 422, 424, respectively, theradiation of heat is performed from both surfaces 401 a, 401 b of thechips 411, 412. Therefore, the radiation property is also sufficient.

Furthermore, the radiation surface 409 is electrically insulated fromthe chips 411, 412 by the DBC substrate 404 that is an insulatingsubstrate disposed inside the semiconductor device. Therefore, there isno need to consider electrical insulation when the radiation surface 409is bonded to the outside cooling member. Also, the one insulatingsubstrate 404 can secure electrical insulation from both the first andsecond surfaces 401 a, 401 b of the chips.

In this embodiment, although the radiation surface 409 is provided atthe side of the second surfaces 401 b of the chips 411, 412, the otherportion can assist the radiation of heat. For example, the thirdradiation member 423 may be partially exposed from the resin 400 toassist the radiation of heat. The electrode 115 formed on the secondsurfaces 401 b of the chips 411, 412 needs not be made of pure Al toprotect the devices of the chips 411, 412. The first to third radiationmembers 421 to 423 are separate members, and are integrally bonded toform the first side radiation member 420 by soldering in thisembodiment; however, they may be formed as an integrated member.

The electrodes for the FWD 412 need not be formed from pure Al if noproblem occurs concerning thermal stress or the like. When the firstside radiation member 420 needs not be electrically insulated from thesecond side radiation member 424, the DBC substrate 404 made of AlN canbe omitted. The DBC substrate 404 can dispense with the land 453 if theland 113 of the IGBT 411 can be wire-bonded to the gate terminal 408directly.

(Seventeenth Embodiment)

A semiconductor device in a seventeenth preferred embodiment is shown inFIGS. 27, 28A and 28B. As shown in the figures, in this embodiment,first side and second side radiation members 503, 504 are bonded to twoSi chips 501 a, 501 b, which are arranged on a plane, through a bondingmember 502 having thermal conductivity to sandwich the chips 501 a, 501b.

The first side radiation member 503 is boned to surfaces (firstsurfaces) 505 a of the Si chips 501 a, 501 b to which wire bonding isperformed, and the second side radiation member 504 is bonded to theother surfaces (second surfaces) 505 b of the Si chips 501 a, 501 b atan opposite side of the surfaces 505 a. In FIG. 27, portions of thesecond side radiation member 504 where it overlaps with other membersare indicated with two-dot chain lines, and portions of the Si chips 501a, 501 b where they overlap with other members are indicated withone-doe chain lines.

In this embodiment, the Si chip wire-bonded in FIG. 27 is an IGBT chip501 a, and the other Si chip is a fly-wheel diode chip 501 b. In theIGBT chip 501 a, the first side radiation member 503 serves as anemitter terminal, and the second side radiation member 504 serves as acollector terminal. On the surface of the IGBT chip 501 a facing thefirst side radiation member 503, a control electrode (not shown) forgiving or receiving electrical signals to or from an external is formed,and is wire-bonded to an inner lead 510.

An equivalent circuit of the IGBT chip 501 a is, for example as shown inFIG. 29, which is composed of a collector C, an emitter E, a gate G, acurrent detection terminal Is, an anode A that is a diode terminal forthermosensitivity, and a cathode K.

As shown in FIGS. 27, 28A, and 28B, the plane shape of the first sideradiation member 503 is substantially a rectangle and has strip portions503 a, 503 b respectively extending from opposite corners of therectangle in opposite directions to each other. Besides, the first sideradiation member 503 has convex portions (protruding portion) 506respectively protruding in a thickness direction thereof to faceprincipal electrodes of the Si chips 501 a, 501 b at the side of thesurfaces 505 a. Front ends of the convex portions 506 are flat at alevel that does not interfere with bonding with the Si chips 501 a, 501b, and the shapes of the flat front ends correspond to plane shapes ofthe principal electrodes of the Si chips 501 a, 501 b.

Besides, on the surface of the first side radiation member 503 facingthe Si chips 501 a, 501 b, protruding portions 507 a are provided atthree locations that are at the strip portions 503 a, 503 b and at aninside of one side parallel to the directions in which the stripportions 503 a, 503 b extend. The protruding portions 507 a protrudetoward the side of the Si chips 501 a, 501 b.

The second side radiation member 504 is approximately the same as thefirst side radiation member 503, but has two strip portions 504 a thatare provided at different locations from those of the strip portions 503a of the first side radiation member 503. In the thickness direction,concave portions 508 are provided to fitly accommodate the Si chips 501a, 501 b. The depths of the concave portions 508 are about 0.1 to 0.3mm.

Further, the surface of the second side radiation member 504 facing theSi chips 501 a, 501 b has protruding portions 507 b protruding towardthe side of the Si chips 501 a, 501 b at three locations that are at thestrip portions 504 a, 504 b, and at an inside of one side parallel tothe directions in which the strip portions 504 a, 504 b extend. Theprotruding portions 507 b of the second side radiation member 504 arepositioned not to overlap with the protruding portions 507 a of thefirst side radiation member 503 when they are observed in an upperdirection as shown in FIG. 27.

The first side and second side radiation members 503, 504 are, forexample, made of Cu (copper). The bonding members 502 are made ofmaterial having high thermal conductivity, such as solder, or brazingfiller metal. Then, the surfaces 505 b of the Si chips 501 a, 501 b arefit in the recess portions 508 and bonded to the second side radiationmember 504 through the bonding members 502. The convex portions 506 ofthe first side radiation member 503 are bonded to the principalelectrodes of the surfaces 505 a of the Si chips 501 a, 501 b.

Further, the control electrode of the Si chips 501 a, 501 b iselectrically connected to the inner lead 510 of a lead frame 509 througha wire 511 by wire bonding. In FIG. 27, portions of the lead frame 509overlapping with other portions are indicated with dotted lines. Asdescribed later, the lead frame 509 has six fixation portions 509 a, 509b respectively having holes 512 a, 512 b for receiving the protrudingportions 507 a, 507 b of the first side and second side radiationmembers 503, 504. Here, Al (aluminum), Au (gold), or the like can beused for the wire 511, and Cu, Cu alloy, 42-alloy, or the like can beused for the lead frame 509.

Then, as shown in FIG. 28B, the protruding portions 507 b formed on thesecond side radiation member 504 are fit in the holes 512 b formed inthe fixation portions 509 b of the lead frame 509, and are caulked. Onthe other hand, each of the protruding portions 507 a formed on thefirst side radiation member 503 is fit in each of the holes 512 a formedin the fixation portion 509 a and caulked in a state where a spacer 513is interposed between the first side radiation member 503 and the leadframe 509.

The spacer 513 is a columnar or prismatic metal such as Cu, and has ahole for allowing the protruding portion 507 a to penetrate it. Thespacer 513 positions the first side radiation member 503 with respect tothe Si chips 501 a, 501 b in the thickness direction of the Si chips 501a, 501 b. When the spacer 513 is a prism, for example, it has a squarecross-section with a side of 2 mm, and a thickness of about 0.6 mm.

Further, as shown in FIGS. 27, 28A, and 28B, the Si chips 501 a, 501 b,and the radiation members 503, 504 fixed as described above are sosealed with resin 514 that each surface of the first side and secondside radiation members 503, 504 at an opposite surfaces facing the Sichips 501 a, 501 b are exposed from the resin 514. In FIG. 27, thecontour of the resin 514 is indicated with a broken line. Of the stripportions 503 a, 503 b, 504 a, 504 b of the first side and second sideradiation members 503, 504, the strip portions 503 a, 504 b, whichextend in the direction opposite to the side where the inner lead 510 isconnected, protrude to the outside of the resin 514, and the externallyprotruding strip portions 503 a, 504 b respectively serve as outerelectrodes of the Si chips 501 a, 501 b.

Next, a method for manufacturing the semiconductor substrate isexplained. First, the lead frame 509, and the first side and second sideradiation members 503, 504, as shown in FIGS. 27, 28A, 28B are prepared.The lead frame 509 is formed into a desirable shape by, for example,punching.

FIGS. 30A to 30D schematically show a method for forming the first sideand second side radiation members 503, 504. As shown in FIG. 30A, thefirst side and second side radiation members 503, 504 are cut out of areel-shaped member 515 made of Cu or the like, the convex portions 506are formed on the first side radiation member 503, and the concaveportions 508 are formed on the second side radiation member 504, bypress working using a punch 516 and a die 517 while moving the punch 516in a direction indicated by an arrow F. FIGS. 30B to 30D show a processfor forming the protruding portions 507 a, 507 b. As shown in thefigures, extruding working is performed to form the protruding portions507 a, 507 b by using a punch 518 and a die 519 that has a recess at acenter thereof, and by moving the punch 518 in a direction indicated byarrows H.

Next, the Si chips 501 a, 501 b are assembled with the lead frame 509and the first side and second side radiation members 503, 504 processedas described above. FIG. 31 schematically shows constitutions of therespective members 501 a, 501 b, 502 to 504, and 509 viewed in a sideface direction at this assembling step. As shown in FIG. 31, theprotruding portions 507 b of the second side radiation member 504 areinserted into the holes 512 b of the fixation portions 509 b of the leadframe 509, and are caulked. In the concave portions 508, the Si chips501 a, 501 b are fitly disposed at the side of the surface 505 b throughsolder foils 502 as bonding members.

Besides, solder foils 502 having shapes corresponding to those of therespective principal electrodes are disposed on the surfaces 505 a ofthe Si chips 501 a, 501 b. The spacers 513 are respectively attached tothe protruding portions 507 a of the first side radiation member 503.Then, the protruding portions 507 a are inserted into the holes 512 a ofthe fixation portions 509 a of the lead frame 509, and then caulked.Incidentally, the convex portions 506 of the first side radiation member503 are omitted in FIG. 7.

The caulking fixation at this assembling step is specifically explainedbelow. FIGS. 32A to 32C schematically shows the step for caulkingfixation. As shown in FIGS. 32A and 32B, after the protruding portions507 a; 507 b of the first side and second side radiation members 503,504 are fit in the holes 512 a, 512 b of the fixation portions 509 a,509 b of the lead frame 509, the protruding portions 507 a, 507 bprotruding from the holes 512 a, 512 b are crushed by moving a punch 520in a direction indicated by arrows I. Accordingly, as shown in FIG. 32C,the first side and second side radiation members 503, 504 and the leadframe 509 are fixed to each other.

Successively, the Si chips 501 a, 501 b, the radiation members 503, 504and the lead frame 509 caulked together undergo solder reflow in ahydrogen furnace or the like, so that the members 501 a, 501 b, 503, 504are integrally fixed by soldering. After that, after wire bonding isperformed between the control electrode on the surface 505 a of the IGBTchip 501 and the lead frame 509, sealing by the resin 514 is performedby transfer mold. Accordingly, the insulation between the first side andsecond side radiation members 503, 504 are achieved, and thesemiconductor device in the present embodiment is completed.

According to the present embodiment, because the first side and secondside radiation members 503, 504 are respectively bonded to the bothsurfaces 505 a, 505 b of the Si chips 501 a, 501 b through the bondingmember 502, the radiation property can be improved. Further, the bondingmember 502 is made of adhesive material having high thermal conductivitysuch as solder or brazing filler metal. This further improves theradiation property.

Besides, the Si chips 501 a, 501 b can be fixed to the second sideradiation member 504 by being installed in the recess portions 508 ofthe second side radiation member 504. Further, and the first side andsecond side radiation members 503, 504 can be fixed with the lead frame509 by inserting the protruding portions 507 a, 507 b of the radiationmembers 503, 504 into the holes 512 a, 512 b of the fixation portions509 a, 509 b of the lead frame 509 and caulking them. As a result, therelative positions of these members can be fixed in a direction parallelto the surfaces of the Si chips 501 a, 501 b.

Also, the protruding portions 507 a of the first side radiation member503 are fit in the holes 512 a of the fixation portions 509 a of thelead frame 509 with the spacers 513 interposed between the first sideradiation member 503 and the lead frame 509. Because of this, the firstside radiation member 503 can be fixed to the lead frame 509 whileproviding a mounting space for the Si chips 501 a, 501 b, and furthercan be positioned relatively in the thickness direction of the Si chips501 a, 501 b. Accordingly, the relative positions of the respectivemembers can be fixed in both the surface direction and the thicknessdirection of the Si chips 501 a, 501 b. The semiconductor device can beprovided with decreased variations in mounting positions of the members.

When a power element such as an IGBT is used as a semiconductor chip asin the present embodiment, there may arise the following problemregarding insulation. FIG. 33 shows an example of an IGBT.

As shown in FIG. 33, a power element such as an IGBT is formed with aguard ring 521 and an EQR (equipotential ring) 522 at an edge portionthereof, and the guard ring 521 and the EQR 522 are formed to haveapproximately the same potential as that of a collector electrode 523.The guard ring 521 and the EQR 522 are further formed on the surface ofthe power element where an emitter electrode 524 is formed. That is, theguard ring 521 and the EQR 522 equipotential with the collectorelectrode 523 exist in the vicinity of the emitter electrode 524.

Therefore, in a case of the power element in which a potentialdifference between the emitter electrode 524 and the collector electrode523 is, for example, about 600 V, the potential difference between theguard ring 521, the EQR 522, and the emitter electrode 524 becomes alsoabout 600 V. Because of this, if a radiation member 525 is positionederroneously and shifted from an accurate position to the side of theguard ring 521 and the EQR 522 as shown in an arrow J in FIG. 33, theguard ring 521 and the EQR 522 might electrically communicate with theemitter electrode 524 through a bonding member 526 such as solder andthe radiation member 525 directly or by discharge. Even if the guardring 521 and the EQR 522 are covered with a protective film 527 made ofpolyimide or the like, the thickness of the film is about 1 to 2 μm atmost, and the withstand voltage to 600 V cannot be secured.

To the contrary, in the semiconductor device of the present embodiment,as described above, in the state where the relative positions of the Sichips 501 a, 501 b, the lead frame 509, and the first side and secondside radiation members 503, 504 are fixed, the convex portions 506 ofthe first side radiation member 503 are bonded to the principalelectrodes on the surfaces 505 a of the Si chips 501 a, 501 b. Becauseof this, the first side radiation member 503 can be brought in contactwith only the principal electrodes by controlling the shape of theconvex portions 506. This can also solve the problem concerning theinsulation, caused by the deviation of the relative position of theradiation member 503 from the Si chips 501 a, 501 b.

The present embodiment exemplifies the example in which the spacers 513are fitly attached to the protruding portions 507 a of the first sideradiation member 503; however, the protruding portions 507 a, 507 b maybe formed in a stepped shape on the respective radiation members 503,504 by, for example, forming the die 519 used for extruding processingshown in FIGS. 32B and 32C to have a stepped portion in the recessportion thereof. Thus, the spacers may be integrated with the protrudingportions.

Besides, the spacers 513 are not limited to be attached to theprotruding portions 507 a of the first side radiation member 503, butmay be attached to the protruding portion 507 b of the second sideradiation member 504 to fix the relative positions of the Si chips 501a, 501 b, the radiation members 503, 504, and the lead frame 509 in thethickness direction of the Si chips 501 a, 501 b.

As in the present embodiment, when both the first side and second sideradiation members 503, 504 are respectively fixed to the lead frame 509by caulking, the variations in mounting positions of the semiconductorchips can be securely suppressed. However, only one of the radiationmembers 503, 504 may be fixed by caulking so long as the positioningaccuracy of the radiation members 503, 504 is improved and thevariations in mounting positions of the semiconductor chips aresuppressed.

Each of the radiation members 503, 504 has a surface externally exposedat an opposite side of the Si chips 501 a, 501 b. The exposed surfacemay be brought in contact with a cooling member for accelerating theradiation of heat. The present embodiment exemplified the IGBT chip 501a as a semiconductor chip, and is so constructed that the variations inmounting position of the semiconductor chip is suppressed. Even when theradiation members 503, 504 are not used as electrodes, the constitutionof the present invention is effective to improve the radiation propertyand to prevent the variations in mounting position of the semiconductorchip.

The spacers 513 are attached to all (three in the present embodiment) ofthe protruding portions 507 a formed on the first side radiation member503; however, the spacers provided at two locations are sufficient tofix the relative positions between the first side radiation member 503and the Si chips 501 a, 501 b in the thickness direction of the Si chips501 a, 501 b. The bonding members 502 are not limited to the solderfoils, but may be solder paste or the like. The semiconductor deviceneeds not always have the two semiconductor chips 501 a, 501 b, and haveonly to have one chip.

(Eighteenth Embodiment)

When the current capacity of the IGBT chip 501 a exceeds 100A, the chipsize is increased, and there is a case the chip size becomes 10 to 16mm. When the radiation members 503, 504 are made of Cu in such a case,since the linear expansion coefficient of Cu is 5 to 6 times larger thanthat of Si constituting the IGBT chip 501 a, solder constituting thebonding member 502 is thermally fatigued in a thermal cycle. This mayresults in occurrence of cracks, increase in thermal resistance, anddeterioration in the heat radiation property.

In this connection, an eighteenth preferred embodiment of the presentinvention has been made as follows. In this embodiment, the first sideand second side radiation members 503, 504 are made of materialdifferent from that of the first embodiment. Hereinafter, differentportions from those in the seventeenth embodiment are mainly described,and the same parts as those in the seventeenth embodiment are assignedto the same reference numerals.

As shown in FIG. 34, as the first side and second side radiation members503, 504, metal having a leaner expansion coefficient similar to that ofSi chips 501 a, 501 b is used. Specifically, as an example, clad members(CICs) each of which is so constructed that a member (invar member) 528made of invar is sandwiched by members (Cu members) 529 made of Cu areadopted. The linear expansion coefficient of each CIC is approached tothat of Si as close as possible by controlling the ratio in thicknessbetween the invar member 528 and the Cu members 529, and the totalthickness. The other members and features such as shapes aresubstantially the same as those in the seventeenth embodiment.

According to the eighteenth embodiment, because the linear expansioncoefficient of the first side and second side radiation members 503, 504is approximated to that of the Si chips 501 a, 501 b, even when eachsize of the chips 501 a, 501 b is large, thermal stress that is causedby the difference in thermal expansion coefficient between the Si chips501 a, 501 b and the radiation members 503, 504 can be suppressed, andconcentration of strain on the bonding members 502 can also beprevented. This prevents the deterioration in bonding property betweenthe radiation members 503, 504 and the Si chips 501 a, 501 b. Inconsequence, the deterioration in radiation property and the decrease inelectrical conductivity when the radiation members 503, 504 are used aselectrodes can also be prevented.

The same effects as described above can be exhibited when Mo(molybdenum) is used in place of invar. In the radiation members 503,504, the members 528 sandwiched by the Cu members 529 need not beunified to the invar or Mo member, and may be different from each other.The radiation members 503, 504 are not limited to the clad members, butmay be other members such as Cu—Mo alloy having a linear expansioncoefficient approximated to that of Si.

Incidentally, the eighteenth embodiment indicates an example using metalhaving a linear expansion coefficient approximated to that of Si, forthe radiation members 503, 504, and adopts the clad members such as CICas an example. However, thermal conductivities of invar and Mo areinferior to that of Cu, and the invar or Mo members 528 lower theradiation property in the thickness direction of the Si chips 501 a, 501b. The following modified embodiment solves this problem.

In this modified embodiment, as shown in FIGS. 35A and 35B, severalinvar members 528 are partially layered in the Cu member 529. FIG. 35Ashows a cross-sectional view showing the radiation member 503, 504 cutin a direction parallel to the layer where it includes the invar members528, while FIG. 35B shows a cross-sectional view showing the radiationmember 503, 504, cut in a direction perpendicular to the layer where itincludes the invar members 528.

As shown in FIGS. 35A and 35B, in this modified embodiment, the invarmembers 528 are provided at several (four) positions inside the Cumember 529. Accordingly, the radiation member 503, 504 has portions thatare composed of only the Cu member 529 in the thickness directionthereof, so that the thermal conductivity in the thickness direction ofthe radiation member 503, 504 are not lessened. Thus, the radiationmember approximated to Si in thermal expansion coefficient can beprovided with sufficient radiation property. In this modifiedembodiment, although the invar members 528 are provided at fourpositions inside the Cu member 529, the invar members 528 may be formedinto a fine mesh by, for example, providing many small sized invarparts. Mo members can be used in place of the invar members. Otherwise,the invar members and the Mo members are used simultaneously.

FIG. 36 shows a semiconductor device as another modified embodiment. Inthe seventeenth and eighteenth embodiment described above, the controlelectrode on the surface 505 a of the IGBT chip 501 a is electricallyconnected to the inner lead 510 by wire bonding; however, as shown inFIG. 36, the connection may be made by a bump-shaped bonding member 530made of solder or the like. Accordingly, when soldering is performedbetween the first side and second side radiation members 503, 504 andthe Si chips 501 a, 501 b, the connection between the inner lead 510 andthe control electrode can be formed simultaneously. This results insimplification of the manufacturing process.

While the present invention has been shown and described with referenceto the foregoing preferred embodiments, it will be apparent to thoseskilled in the art that changes in form and detail may be made thereinwithout departing from the scope of the invention as defined in theappended claims.

What is claimed is:
 1. A semiconductor device comprising: asemiconductor chip; first and second radiation members thermally andelectrically connected to the semiconductor chip interposedtherebetween, and having a radiation surface for radiating heat from thesemiconductor chip; and bump shaped banding members formed on a surfaceof one of the first and second radiation members; and a Resist AssistBonding resin disposed in spaces between the bump shaped bondingmembers.
 2. The semiconductor device of claim 1, wherein the first andsecond radiation members are made of metallic material that is superiorto tungsten and molybdenum in at least one of an electrical conductivityand a thermal conductivity.